Search Results (210)

Chromium-molybdenum steels are extensively used in manufacturing large-volume seamless hydrogen storage vessels, but they still suffer from the hydrogen embrittlement problem. In this study, electrochemical cathodic hydrogen charging is utilized to investigate the hydrogen embrittlement of 4130X steels, with emphasis on the influence of charging current density and temperature on hydrogen permeation and hydrogen embrittlement susceptibility. The hydrogen penetration rate and hydrogen diffusion coefficient of 4130X steel both increase with an increase in hydrogen-charging current density and temperature. The results demonstrate that the degree of hydrogen-induced degradation in tensile ductility is more marked with increasing hydrogen-charging current density, while the hydrogen embrittlement index exhibits a peak at a temperature of 308 K, in which brittle patterns like quasi-cleavage surfaces and crack formations occur. These findings are crucial for understanding hydrogen-induced embrittlement and determining test temperatures of hydrogen-related engineering material applications. Full article

The strength parameters of fault gouge are critical factors that influence sealing capacity and fault reactivation in underground gas storage reservoirs. This study investigates the shear characteristics of remolded fault gouge under varying hydro-mechanical conditions, focusing on the coupled influence of water content and cementation. Sixty fault gouge samples are prepared using a mineral mixture of quartz, montmorillonite, and kaolinite, with five levels of water content (10–30%) and three cementation degrees (0%, 1%, 3%). Direct shear tests are conducted under four normal stress levels (100–400 kPa), and microstructural characteristics are examined using SEM. The results show that shear strength and cohesion exhibit a non-monotonic trend with water content, increasing initially and then decreasing, while the internal friction angle decreases continuously. Higher cementation degrees not only enhance shear strength and reduce the softening effect caused by water but also shift the failure mode from ductile sliding to brittle, cliff-type rupture. Moreover, clay content is found to modulate the degree—but not the trend—of strength parameter responses to water and cementation variations. Based on the observed mechanical behavior, a semi-empirical shear strength prediction model is developed by extending the classical Mohr–Coulomb criterion with water–cementation coupling terms. The model accurately predicts cohesion and internal friction angle as functions of water content and cementation degree, achieving strong agreement with experimental results (R² = 0.8309 for training and R² = 0.8172 for testing). These findings provide a practical and interpretable framework for predicting the mechanical response of fault gouge under complex geological conditions. Full article

Polypropylene (PP), with its good physical, thermal, and mechanical properties and excellent processing capabilities, has become one of the most used synthetic polymers. It is known that the overall properties of semicrystalline polymers, including PP, are governed by morphology, which is influenced by the crystallization behavior of the polymer under specific conditions. The most important industrial PP remains the isotactic one, and it has been studied extensively for its polymorphic characteristics and crystallization behavior for over half a century. Due to its regular chain structure, isotactic polypropylene (iPP) belongs to the group of polymers with a high tendency for crystallization. The rapid quenching of molten iPP fails to produce a completely amorphous polymer but leads to an intermediate crystalline order. On the other hand, slow cooling yields a material with high crystalline content. The processing conditions that occur in practice and industry are between these two extremes and, in some cases, are even very close. Therefore, the study of limits in processability and the impact of extreme preparation conditions on morphology, structure, thermal, and mechanical properties fills a gap in the current understanding of how the processing conditions of iPP can be used to design the desired properties for specific applications and is in the focus of this research. The first set of samples (Q samples) was obtained by rapid quenching, while the second was prepared by very slow cooling from the melt to room temperature (SC samples). Testing of samples was performed by optical microscopy (OM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic dielectric spectroscopy (DDS), and mechanical measurements. Characterization revealed that slowly cooled samples exhibited a significantly higher degree of crystallinity and larger crystallites (χ ≥ 55% and L₍₁₁₀₎ ≈ 20 nm), compared to quenched samples (χ < 30%, L₍₁₁₀₎ ≤ 3 nm). Mechanical testing showed a drastic contrast: quenched samples exhibited elongation at break > 500%, while slowly cooled samples broke below 15%, reflecting their brittle behavior. For the first time, DDS is applied to investigate molecular mobility differences between processing-dependent structural forms, specifically the mesomorphic (smectic) and α-monoclinic forms. In slowly cooled samples, α relaxation exhibited both enhanced intensity and an upward temperature shift, indicating stronger structural constraints due to a much higher crystalline phase content and significantly larger crystallite size, respectively. These findings provide novel insights into the structure–property–processing relationship, which is crucial for industrial applications. Full article

A fabric orientation angle has a significant influence on the failure mechanisms at the lamina level. Any change in this angle can lead to a sudden reduction in strength, potentially resulting in catastrophic failures due to variations in load-carrying capacity. This study examined the impact of off-axis fabric orientation angles (0°, 15°, 30°, 45°, 60°, and 90°) on the flexural properties of non-crimp basalt-fibre-reinforced acrylic thermoplastic composites. The basalt/Elium^® composite panels were manufactured using a vacuum-assisted resin transfer moulding technique. The results show that the on-axis (0°) composite specimens exhibited linear stress–strain behaviour and quasi-brittle failure characterised by fibre dominance, achieving superior strength and failure strain values of 1128 MPa and 3.85%, respectively. In contrast, the off-axis specimens exhibited highly nonlinear ductile behaviour. They failed at lower load values due to matrix dominance, with strength and failure strain values of 144 MPa and 6.0%, respectively, observed at a fabric orientation angle of 45°. The in-plane shear stress associated with off-axis angles influenced the flexural properties. Additionally, the degree of deformation and the fracture mechanisms were analysed. Full article

It has been known for some time that grading of the elastic modulus (namely, softer in the surface) leads to a significant reduction in tensile stresses due to contact loadings; this has been studied mostly to suppress the cracking of brittle materials. In particular, a recent study has demonstrated that the effect is most pronounced for a large Poisson’s ratio, as is the case for incompressible materials. Grading of the modulus occurs intrinsically in viscoelastic materials like rubber when there is a temperature gradient within the rubber, which leads to significant changes of tensile stresses, affecting fatigue and wear. Friction and wear have been analyzed experimentally in the past with respect to mean temperature, revealing an ideal range of temperature with the highest friction and lowest wear, but the effect of the temperature gradient is not as well understood. The present paper presents a simple model of a sinusoidal wave of pressure and shear traction moving on a viscoelastic half-plane (standard material) at constant velocity, finding an approximate solution for a linear variation of viscosity across the depth. We find that tensile stresses may be very significantly altered by temperature changes of a few degrees only across the depth equal to the wavelength of the loading wave. In particular, they are reduced if the temperature decreases with depth, with beneficial effects for fatigue and wear. Full article

Abrasive waterjet technology is a promising sustainable and green technology for cutting underground structures. Abrasive waterjet usage in demolition promotes sustainable and green construction practices by reduction of noise, dust, secondary waste, and disturbances to the surrounding infrastructure. In this study, a numerical framework based on a coupled Smoothed Particle Hydrodynamics (SPH)–Finite Element Method (FEM) algorithm incorporating the Riedel–Hiermaier–Thoma (RHT) constitutive model is proposed to investigate the damage mechanism of concrete subjected to abrasive waterjet. Numerical simulation results show a stratified damage observation in the concrete, consisting of a crushing zone (plastic damage), crack formation zone (plastic and brittle damage), and crack propagation zone (brittle damage). Furthermore, concrete undergoes plastic failure when the shear stress on an element exceeds 5 MPa. Brittle failure due to tensile stress occurs only when both the maximum principal stress (σ₁) and the minimum principal stress (σ₃) are greater than zero at the same time. The damage degree ($\chi$) of the concrete is observed to increase with jet diameter, concentration of abrasive particles, and velocity of jet. A series of orthogonal tests are performed to analyze the influence of velocity of jet, concentration of abrasive particles, and jet diameter on the damage degree and impact depth (h). The parametric numerical studies indicates that jet diameter has the most significant influence on damage degree, followed by abrasive concentration and jet velocity, respectively, whereas the primary determinant of impact depth is the abrasive concentration followed by jet velocity and jet diameter. Based on the parametric analysis, two optimized abrasive waterjet configurations are proposed: one tailored for rock fragmentation in tunnel boring machine (TBM) operations; and another for cutting reinforced concrete piles in shield tunneling applications. These configurations aim to enhance the efficiency and sustainability of excavation and tunneling processes through improved material removal performance and reduced mechanical wear. Full article

Efficient and low-loss harvesting methods are crucial for preserving the postharvest quality of the first crop of goji berries grown in saline–alkali soils. However, as a brittle horticultural fruit rich in diverse bioactive compounds, goji berries are highly vulnerable to mechanical damage during harvesting, which adversely affects their storability and subsequent processing. To address this challenge, a multi-degree-of-freedom vibration model was developed based on the growth characteristics of first-crop organic goji berry fruit-bearing branches in the Qinghai region. The dynamic response of the branches under various excitation conditions was simulated, and the effects of excitation position, frequency, force amplitude, and phase angle on the fruit detachment rate, impurity rate, and breakage rate were systematically analyzed. Based on both the simulation and experimental results, a response surface methodology (RSM) was employed to optimize the picking parameters. The results of the field experiment showed that under the optimal conditions of vibration excitation in the ripe fruit area, a frequency of 5.7 Hz, an amplitude of excitation force of 0.27 N, a phase angle of 135°, a fruit picking rate of 97.58%, a miscellaneous content rate of 5.12%, and a breakage rate of 7.66% could be realized. The results of this study help to maintain the postharvest quality of first-crop goji berry fruits in saline–alkali land, and also provide a theoretical basis and practical reference for the optimization of first-crop goji berry harvesting equipment. Full article

Different from general underground engineering, the micro-damage prior to failure of the surrounding rock has a significant influence on the geological disposal of high-level radioactive waste. However, the quantitative research on pre-failure dilatancy damage characteristics and stress path influence of hard brittle rocks under high stress levels is insufficient currently, and especially, the stress path under simultaneous unloading of axial and confining pressures is rarely discussed. Therefore, three representative mechanical experimental studies were conducted on the Beishan granite in the pre-selected area for high-level radioactive waste (HLW) geological disposal in China, including increasing axial pressure with constant confining pressure (path I), increasing axial pressure with unloading confining pressure (path II), and simultaneous unloading of axial and confining pressures (path III). Using the deviatoric stress ratio as a reference, the evolution laws and characteristics of stress–strain relationships, deformation modulus, generalized Poisson’s ratio, dilatancy index, and dilation angle during the path bifurcation stage were quantitatively analyzed and compared. The results indicate that macro-deformation and the plastic dilatancy process exhibit strong path dependency. The critical value and growth gradient of the dilatancy parameter for path I are both the smallest, and the suppressive effect of the initial confining pressure is the most significant. The dilation gradient of path II is the largest, but the degree of dilatancy before the critical point is the smallest due to its susceptibility to fracture. The critical values of the dilatancy parameters for path III are the highest and are minimally affected by the initial confining pressure, indicating the most significant dilatancy properties. Establish the relationship between the deformation parameters and the crack-induced volumetric strain and define the damage variable accordingly. The critical damage state and the damage accumulation process under various stress paths were examined in detail. The results show that the damage evolution is obviously differentiated with the bifurcation of the stress paths, and three different types of damage curve clusters are formed, indicating that the damage accumulation path is highly dependent on the stress path. The research findings quantitatively reveal the differences in deformation response and damage characteristics of Beishan granite under varying stress paths, providing a foundation for studying the nonlinear mechanical behavior and damage failure mechanisms of hard brittle rock under complex loading conditions. Full article

This study investigates the effects of B₄C content (2.5, 5, 7.5, and 10 wt.%) on the microstructure and wear resistance of laser cladding 316 stainless steel coatings on a 2Cr12MoV steel substrate. The coating was prepared by laser cladding technology. The phase composition, microstructure evolution, microhardness, and tribological properties of the coating were analyzed. The results show that the decomposition of B₄C particles is complete, and the phase composition of the coating includes Austenite, Fe₂₃ (B₃C₃), Cr₂₃ (B_1.5C_4.5), and a Fe-Ni solid solution. The increase in B₄C content significantly increased the microhardness of the material from 206 HV_0.2 (substrate) to 829 HV_0.2 (10 wt.% B₄C) by 4.02 times. Wear resistance also improved, with the 10 wt.% coating exhibiting the lowest wear rate (10 × 10⁻⁸ mm³/N·m) due to fine-grained and dispersion strengthening mechanisms. However, excessive B₄C (10 wt.%) induced cracks from increased brittleness, resulting in higher friction coefficients. The wear mechanism consists of fatigue wear, adhesive wear, and oxidative wear, and the degree of wear decreases with the increase in B₄C content. This work demonstrates that the addition of B₄C effectively improves the hardness and wear resistance of 316 stainless steel coatings, providing practical insights into surface engineering in high wear applications. Full article

Recently, shallow gas fields and hydrate-bearing sand in the deepwater area of the northern South China Sea have been successively discovered, and the accurate prediction of shallow sands is an important foundation. However, most of the current prediction methods are mainly for deep oil and gas reservoirs. Compared with those reservoirs with high degree of consolidation, shallow sandy reservoirs are loose and unconsolidated, whose geophysical characteristics are not well understood. This paper analyzes the logging data of shallow sandy reservoirs recovered in the South China Sea recently, which show that the sand content has a significant influence on Young’s modulus and Poisson’s ratio of the sediments. Therefore, this paper firstly constructs a new petrophysical model of unconsolidated strata targeting sandy content and qualitatively links the mineral composition and the elastic parameters of the shallow marine sediments and defines a new indicator for sandy content: the modified brittleness index (MBI). The effectiveness of MBI in predicting sandy content is then verified by measured well data. Based on pre-stack seismic inversion, the MBI is then inverted, which will identify the sandy deposits. The method proposed provides technical support for the subsequent shallow gas and hydrate exploration in the South China Sea. Full article

Targeting the engineering properties of poor strength and susceptibility to damage in roadbeds and slopes within clay regions, xanthan gum is employed as a soil enhancer, concurrently addressing the issue of the low utilization rate of plant coir fiber. The unconfined compressive strength test (UCS) is used to analyze the influence of different maintenance methods, maintenance duration, xanthan gum dosage, and coconut fiber dosage on the mechanical properties of the enhanced soil. Furthermore, based on scanning electron microscope (SEM) tests, the underlying mechanisms governing the mechanical properties of fiber-reinforced xanthan gum-improved soil are uncovered. The results indicated that the compressive strength of amended soil is significantly enhanced by the incorporation of xanthan gum and coir fiber. After 28 days of conditioning, the compressive strength of the amended soil under dry conditions (conditioned in air) was significantly higher (3 MPa) than that under moist conditions (conditioned in plastic wrap) (0.57 MPa). Xanthan gum influenced both the compressive strength of the specimens and the degree of strength enhancement, whereas coir fibers not only augmented the strength of the specimens but also converted them from brittle to ductile, thereby imparting residual strength post-destruction. Microscopic analysis indicates that the incorporation of xanthan gum and coconut shell fiber significantly diminishes the number of pores and cracks within the soil matrix, while enhancing the internal inter-particle cementation. This synergistic effect contributes to soil improvement, providing theoretical and technical guidance for roadbed enhancement and slope repair. Full article

The present study focuses on the mechanical performances of basalt fiber-reinforced composites based on the more environmentally friendly Recyclamine^® resin (BR) and conventional and widely used room-cured epoxy systems (BE). Specifically, the study probes the tensile and compressive responses of the composites fabricated by vacuum-assisted resin transfer molding. Experimental results revealed that the tensile strength of basalt–Recyclamine was higher than its counterpart (464 MPa compared to 390.9 MPa). At the same time, the BR performed only marginally better under compression, with a strength of 237.7 MPa compared to 233.9 MPa for BE. However, the BR demonstrated significantly enhanced ductility reflected by its greater compressive strain capacity (3.9% compared to only 1.1%). Different microscopic analyses unveiled distinct failure mechanisms, with more progressive failure patterns observed in BR compared with the brittle fracture characteristics of the BE composite. The performance of several micromechanical models was also investigated, with their results corroborating with the experimental results with varying degrees of accuracy. The statistical analysis showed great consistency in the results, with the CoV value below 10%. Experimental results indicated that the basalt–Recyclamine composites can be considered a promising sustainable alternative to traditional polymeric resin-based systems due to their balanced mechanical performance and environmental advantages. Full article

In nature, many brittle materials contain natural defects such as microcracks or joints, for example, rocks. Under water-saturated conditions, the strength of defective materials undergoes varying degrees of attenuation, leading to material failure and even structural instability in engineering contexts. Moreover, the deformation and failure of defective brittle materials are essentially the result of the accumulation and dissipation of energy. Studying the energy evolution of defective brittle materials under load is more conducive to reflecting the intrinsic characteristics of strength changes and overall failure of brittle materials under external loading. Natural defective brittle rock materials were firstly water saturated and triaxial compression tests were performed to determine the mechanical properties of water-saturated materials. The energy evolution patterns of water-saturated materials under varying confining pressures were also obtained. Using the discrete element method, the macro- and micro-failure characteristics of water-saturated materials were investigated, revealing the mesoscopic mechanisms of deformation and failure evolution in these materials. The results indicate that confining pressure significantly enhances the peak compressive strength and elastic modulus of water-saturated defective materials. When the confining pressure increased from 0 MPa to 20 MPa, the peak strength and elastic modulus of the water-saturated materials increased by 126.8% and 91.9%, respectively. Confining pressure restricts the radial deformation of water-saturated materials and dominates the failure mode. As confining pressure increases, the failure mode transitions from tensile splitting (at 0 MPa confining pressure) to shear failure (at confining pressures ≥ 10 MPa), with the failure plane angle gradually decreasing as confining pressure rises. Confining pressure significantly alters the energy storage–release mechanism of water-saturated defective brittle materials. At peak load, the total energy, elastic energy, and dissipated energy increased by 347%, 321%, and 1028%, respectively. The ratio of elastic energy storage to peak strain ratio shows a positive correlation, and the elastic storage ratio of water-saturated defective brittle materials under confining pressure is always higher than that without confining pressure. When the strain ratio exceeds 0.94, a negative correlation between confining pressure and the rate of elastic storage ratio is observed. From the perspective of mesoscopic fracture evolution in water-saturated defective brittle materials, the crack propagation path shifts from the periphery to the center of the material, and the fracture angle decreases linearly from 89° to 58° as confining pressure increases. The dominant direction of crack development is concentrated within the 45–135° range. The findings elucidate the mechanisms by which water saturation and confining pressure influence the strength degradation of natural defective brittle materials from both mesoscopic and energy perspectives, providing theoretical support for the stability control of related engineering structures. Full article

The mechanical properties of PBT-based azide propellants, composed of a 3,3′-bis(azidomethyl)oxetane/tetrahydrofuran (PBT) copolymer matrix and defective ammonium perchlorate (AP) crystals, are significantly influenced by the matrix–crystal interface. This study employed molecular dynamics (MD) simulations to examine interfacial effects on mechanical performance under uniaxial tensile deformation. Models with varying cross-linking densities (70%, 80%, 90%) and AP defect widths (20 Å, 30 Å, 40 Å) were analyzed to assess the effects of temperature, strain rate, cross-linking degree, and defect size on interfacial adhesion strength and failure mechanisms. Results indicate that at low temperatures, the interface exhibited high stress peaks and brittleness characteristics, transitioning to plastic flow and enhanced ductility at higher temperatures. Cross-linking density significantly affects interfacial strength: a 90% cross-linking degree achieved the highest stress peak and optimal tensile resistance, whereas lower cross-linking resulted in weaker stress transfer and accelerated post-peak stress decay. Higher strain rates increased peak stress and shortened deformation times, while lower strain rates promoted molecular rearrangement, enhancing tensile resistance. Defect size also plays a crucial role, with smaller defects maintaining interfacial dominance, whereas larger defects shift failure toward the bulk matrix, reducing stress transfer efficiency. These findings provide atomic-scale insights into interfacial defects and key material parameters, offering theoretical guidance for optimizing the structural stability of composite propellants. Full article

This study is an experiment that looks at what happens when 18 supported reinforced concrete beams with waste glass inside them are put on fire. All the supported beams were tested under a three-point load. We classified the beams into three groups based on the glass-to-sand replacement ratio. Two sand replacement ratios (10% and 20%) were considered and compared with the control beams (without replacement). Two periods of burning were studied to investigate the mechanical properties of ferrocement and the behavior of simply supported beams. We considered a temperature of 550 °C and gradually increased the burning to reach this degree. Mode failure, mechanical properties, and load–deflection were present in this study. According to this study and its results, it seems that approximately all mode failures were compound flexural and shear failures. The flexural and compressive strength of replacing sand with glass concrete leads to an improvement in the flexural behavior of the reinforced concrete beam incorporating waste glass (brittle failure) that happened when burning the beam element without sand replacement glasses. The replacement ratio (10%) is the best value of the replacement ratio of the glasses; the compressive strength increased by about 10% to 29% by the replacement ratio. When replacing 10% of the sand with glasses, the ratio increases from 1% to 16%, but the compressive strength decreases from 20% to 51% when the burning time increases from one hour to an hour and a half. When 10% of the sand is replaced by glasses by weight, the first crack load capacity goes up by about 8% for one hour of burning and by 16% for one hour and a half of burning compared to beams that are not burning. The ultimate load capacity also goes up by about 17.5% for one hour of burning and by 23.5% for one hour and a half of burning compared to beams that are not burning. Otherwise, sand replacement was 10% by glasses; by weight, the ultimate load strength increased about 6% when the burning was one hour and 12% when the burning was one hour and a half compared with the beams without burning for the same phase. Full article