Decrease In Strength Research Articles

Effect of boiling water soaking on the mechanical properties and durability of nanoclay-enhanced bamboo and glass fiber epoxy composites

Fiber-reinforced polymer composites are subjected to harsh environmental conditions over the course of their designed lifespan. Studying the aging process of fiber-reinforced polymer composites exposed to boiling water is critical for improving their durability. This study uses a hand lay-up technique to fabricate composites from glass fiber, bamboo fiber, nanoclay, and epoxy. Tensile and flexural tests are conducted following ASTM standards. The % of water uptake of the boiling water-soaked specimens is measured, and the performance of the dry composites is compared with those of boiling water-soaked composites. The results show that boiling water-soaking conditions have an adverse impact on all the composites. Boiling water-soaked epoxy samples show a reduction in tensile properties by 25 and 30% and flexural properties by 18 and 22% under processes 1 and 2 of boiling water soaking, respectively, compared to dry ones. Meanwhile, for fiber-reinforced composites, the tensile properties decrease by 19 and 27%, and the flexural properties decline by 12 and 20% under processes 1 and 2 of boiling soaking, respectively. However, incorporating nanoclay enhances the tensile and flexural properties of the epoxy and the composites by 5 to 7% and 10 to 12%, respectively. The water absorption rate and the impact of boiling water-soaking on composite strength decrease with the addition of nanoclay. Additionally, nanoclay reduces the percentage of reduction in tensile properties by 17 and 26% and in flexural properties by 11 and 18% under processes 1 and 2 of boiling soaking, respectively. SEM analysis of the fracture surfaces reveals the causes of specimen failure under tensile load, with distinct differences between dry and boiling water-soaked specimens.

Microstructure and mechanical properties of dissimilar resistance spot welds of TBF and HSLA300 steel sheets

Abstract The welding behavior of the resistance spot welded dissimilar TBF–HSLA300 steel joints under different welding parameters was investigated. TBF steels were used as galvanized or ungalvanized. Microstructural characterization and mechanical tests were performed. Higher heat input resulted in the higher possibility of shrinkage cavities at the weld nugget and also increased the risk of liquid metal embrittlement (LEM) crack in the heat affected zone (HAZ) on galvanized TBF steel sheets. A partial melting zone was observed on HSLA300 side. The welds with ungalvanized TBF sheets had the higher nugget size and indentation. The highest hardness values (over 500 HV0.1) were observed in HAZ on TBF side. The lowest hardness values (below 300 HV0.1) on TBF side were observed in a very narrow softening zone between tempered zone and base metal. The fractures of all spot welds in the tensile shear test occurred on the TBF steel side with the thinner thickness. Low-strength steel sheet have to be sufficiently thicker in order to achieve higher welding strength. Higher welding time led to higher weld strength in the ungalvanized TBF combination. In the galvanized TBF combination, higher heat input led to the drastic decrease in weld strength due to LEM cracks.

Microstructure Evolution of Extruded TiAl Alloy During Vacuum Isothermal Superplastic Forging Process

Vacuum isothermal forging is an ideal method for preparing high-performance TiAl alloy forgings, as it is carried out under the conditions of a uniform temperature field and oxygen isolation. The mechanical properties of TiAl alloys strongly depend on their microstructure, so it is important to study their microstructure evolution during the forging process to improve their properties. In this study, TiAl alloy forgings with different deformations were produced from the extruded billets by vacuum isothermal superplastic forging under lower temperatures and extremely low strain rate conditions. The results indicate that the streamlined structure in the extruded alloy was destroyed during the forging process. As the deformation increased, the dynamic recrystallization was more fully carried out, leading to a substantial decrease in remnant lamellar colonies and a significant increase in the γ phase, and the microstructure was transformed from nearly lamellar (NL) to near gamma (NG) structure. The proportion of high-angle grain boundaries (HAGB) increased with increasing deformation, while the grain size reduced from 20 μm to 4.6 μm. In addition, the streamlined features and textures exhibited a weakening trend with increasing deformation, leading to a decrease in the ultimate strength from 891 MPa to 722 MPa. To maintain the streamlined characteristics and retain strengthening effects, the forging deformation should not exceed 56.7%.

Interfacial Shear Fracture Behavior of C18150Cu/1060Al/C18150Cu Trilayered Composite at Different Temperatures

Interfacial shear fracture behavior of C18150Cu/1060Al/C18150Cu trilayered composite at different temperatures, which was fabricated by high-temperature oxygen-free hot rolling technology. The interfacial microstructure, interfacial shear strength, interfacial shear fracture morphology, and microstructure near the shear fracture were systematically investigated. The results reveal that the composite exhibits a metallurgical and mechanical bonding interface, along with mechanical interlocking between the copper and aluminum. As the testing temperature increases, the interfacial shear strength decreases. At temperatures below 150 °C, the strength remains stable, but it sharply decreases at temperatures above 150 °C. Specifically, the interfacial shear strength is 56.8 MPa at room temperature and 20.9 MPa at 350 °C. When the testing temperature is below 100 °C, the interfacial shear fracture predominantly occurs at the interface between the copper alloy and intermetallics. Also, aluminum is attached to the copper surface of the shear fracture, and the size and quantity of attached aluminum increase with the increase in temperature. When the testing temperature exceeds 100 °C, curled aluminum appears on the copper layer, and a large number of intermetallics are attached to the aluminum surface. This indicates that the bonding strength between intermetallics and aluminum is higher than that between intermetallics and copper.

Cracking the Code of Calcification: How Presence and Burden among Intracranial Arteries Influence Stroke Incidence and Recurrence.

Intracranial atherosclerosis accounts for about 8% of all strokes in Western societies but the influence of arterial calcification on plaque instability is a topic on ongoing debate. Explore the association between the presence and burden of calcium in atherosclerotic plaques among intracranial arteries with the risk of clinical or silent stroke events through a systematic review and meta-analysis. Adhering to PRISMA guidelines, studies from PubMed and Embase were analyzed up to May 2024. Adult populations undergoing CT/CTA scans for symptomatic and asymptomatic atherosclerosis among intracranial vessels. Statistical analyses were performed to identify the impact of calcium presence and relative burden on stroke incidence or recurrence. Risk of bias was evaluated with QUADAS-2 criteria while GRADE system was used to assess quality of evidence. The study synthesized data from 8 longitudinal studies, creating two different models: Calcium presence (heterogeneity: Q 9.19; I2 42.61%) and calcium burden (heterogeneity: Q 6.01; I2 0.01%). As for calcium presence and stroke events, 6839 patients were considered, and two statistical models were made. Our analysis established a significant association between the presence of calcium and stroke events. [OR= 1.54, 95% CI 1.06, 2.24, p=0.001]. A subsequent effect size analysis showed a similar correlation's strength [OR = 1.56, 95% CI 1.11, 2.19, p = 0.001]. As for calcium burden and stroke events, 4885 patients were considered with effect size analysis establishing a positive correlation [OR = 1.31, 95% CI, 1.17, 1.46, p =< 0.001). A decrease in correlation strength was found between calcium presence [OR = 1.56] and burden [OR = 1.31] with stroke events. Despite strict exclusion criteria, heterogeneity across studies and between different statistical models of the present study persisted. Valuable data loss among excluded studies could have affected the findings of this meta-analysis. Unified calcium scoring pattern and individual arterial segment analysis was not widely adopted by included literature. Our meta-analysis showed a weak, yet present association between presence and burden of calcification among intracranial arterial vessels and clinical or silent stroke events. Considering the high prevalence of intracranial calcification in the general population, widespread intracranial calcium assessment for stroke prediction has currently poor evidence. Investigation on specific intracranial vessels or exploration of newer calcium patterns could be essential to enhance the predictive accuracy of calcification in stroke incidence or recurrence. IAC = Intracranial Arterial Calcification; HU = Hounsfield Unit; RE = Random Effect.

Mechanism of Crack Development and Strength Deterioration in Controlled Low-Strength Material in Dry Environment

The continuous expansion at the urban scale has produced a lot of construction waste, which has created increasingly serious problems in the environmental, social, and economic realms. Reuse of this waste can address these problems and is critical for sustainable development. In recent years, construction waste has been extensively recycled and transformed into highly sustainable construction materials called controlled low-strength materials (CLSMs) in backfilling projects, pile foundation treatment, roadbed cushion layers, and other applications. However, CLSMs often experience shrinkage and cracking due to water loss influenced by climatic temperature factors, which can pose safety and stability risks in various infrastructures. The purpose of this paper was to study the mechanism of crack formation and strength degradation in a CLSM in a dry environment and to analyze the deterioration process of the CLSM at the macro- and micro-scales by using image analysis techniques and scanning electron microscopy (SEM). The test results show that with the drying time, the CLSM samples had different degrees of cracks and unconfined compressive strength (UCS) decreases, and increasing the content of ordinary Portland cement (OPC) reduced the number of cracks. The addition of bentonite with the same OPC content also slowed down the crack development and reduced the loss of UCS. The development of macroscopic cracks and UCS is caused by the microscopic scale, and the weak areas are formed due to water loss in dry environments and the decomposition of gel products, and the integrity of the microstructure is weakened, which is manifested as strength deterioration. This research provides a novel methodology for the reuse of construction waste, thereby offering a novel trajectory for the sustainable progression of construction projects.

The Results of the Research and Experimental verification of the Program for improving the Sambo Wrestling Technique of Veteran Athletes

The need for Martial Arts training for men of older age groups is due to the numerous physical, psychological and social benefits that these practices provide in the conditions of age changes. Regular training improves the cardiovascular system, increases general endurance and strengthens immunity. Martial Arts have a powerful effect on the psychological state, helping to combat stress, anxiety and depression, which can increase with age. In turn, the urgency of improving the Technical Preparation of fellow Veteran Wrestlers lies in the fact that with age, the physical capabilities of athletes change, reaction speed, endurance and strength decrease. However, maintaining and developing technical skills is a key factor in maintaining a high level of sportsmanship. The article presents the Results of the Research and Experimental verification of the Program for improving the Sambo Wrestling Technique for Veteran Wrestlers, which is based on the emphasized use of Modern Technical means of training. The Purpose of the study was to develop and implement a Program that would ensure effective improvement of the Technical Skills of veteran Sambo Wrestlers, taking into account their physical and age characteristics. The Pedagogical Experiment showed a positive effect of the use of Modern Technical means on improving the Technical Preparation of veteran Sambo Wrestlers, which is confirmed by statistically significant Results. The conclusions of the study indicate the expediency of implementing similar Programs to increase the effectiveness of the Educational and Training Process of Veteran Sambo Wrestlers.

Relevance of body weight adaptation and modern obesity-defining parameters in the analysis of isokinetic trunk strength in people with obesity - A retrospective analysis.

Pathologic values of body mass index (BMI), body weight, and waist circumference correlate with higher absolute and lower relative trunk strength. Whether waist-to-height ratio (WHtR) is appropriate for showing trunk strength differences in people with obesity and whether a continuous linear relationship exists between the increase in obesity and trunk strength is unknown. This retrospective cross-sectional study included 1174 subjects (1114 men and 60 women). Measured values included body weight, height, waist circumference, WHtR, BMI, and both absolute and body weight-adapted trunk flexor/extensor strength. Statistical analyses included t-tests, Welch tests, Pearson correlations, mixed-linear, and nonlinear regression analyses. Positive correlations with absolute trunk strength were found in subjects without obesity for all anthropometric parameters except WHtR. Weaker positive and partly negative correlation and linear regression coefficients were found in subjects with obesity. Nonlinear relationships were found between age, BMI, WHtR, and absolute respective body weight-adapted trunk strength. The relationship between obesity-defining measures/ indices and trunk strength is non-linear. Increasing BMI, waist circumference, or WHtR above cut-off values known from cardiovascular research is linked to a decrease or weaker increase in trunk strength. Body weight adaptation is recommended to avoid misinterpretation of apparently good absolute trunk strength values in people with obesity.

Exploring the coupled effects of interfaces and grain size gradients in heterogeneous laminate and gradient structures via a multiple mechanism based constitutive model

Abstract As two promising types of heterogeneous materials, gradient structures and heterogeneous laminates possess superior mechanical properties, such as a combination of high strength and exceptional ductility, which can be attributed to back stress strengthening and strain hardening arising from their heterogeneous microstructures. Recent efforts have been made to combine these two unique microstructures to further improve their properties and performance. However, how heterogeneous interfaces and grain size gradients interplay with each other remains unknown. Therefore, this work aims at exploring the coupled effects of interfaces and grain size gradients in copper–bronze heterogeneous laminate and gradient samples via multiple mechanism-based constitutive modeling incorporating statistically stored dislocations, geometrically necessary dislocations, back stress and deformation twinning. It is revealed that different grain size gradients have profound influence on the deformation mechanisms and mechanical behaviors of the material: a monotonic grain size gradient in the copper layers strengthens the material yet reduces its ductility as a result of diminished back stress hardening due to weakened interface effects; a symmetric grain size gradient in the bronze layers leads to an increase in ductility and a decrease in strength; only by introducing a symmetric grain size gradient into the copper layers can the strength and ductility of the material be improved simultaneously, which is accredited to stronger back stress and grain boundary strengthening due to the synergistic effects between the interfaces and the grain size gradients. In addition, the distinct propensities for twinning in the copper and bronze layers can be attributed to both their different stacking fault energies and grain sizes.

Effect of different clay additions to concrete on its ultrasonic acoustic parameters and compressive strength

Due to various factors, the concrete may contain mud, a condition that can lead to a decrease in strength and changes in the ultrasonic acoustic parameters of the concrete. In order to study the effect of concrete mud content () on ultrasonic acoustic parameters and compressive strength, this paper firstly derived the relationship equations between concrete mud content and acoustic parameters and compressive strength. Subsequently, the acoustic parameters and compressive strength were tested for concrete specimens with different mud contents cast on site. Finally, the effects of concrete mud content on wave velocity, sound time, amplitude, frequency and strength were analyzed according to the measured acoustic parameters, and the relational equations of mud content on acoustic parameters were verified, which provided a reference for evaluating the defective degree of concrete mud content. The main conclusions are: According to sound field theory, the higher the mud content of concrete, the lower its strength, the higher the sound time value, the lower the sound velocity value, and the smaller the amplitude value. The measured data shows that as the age of concrete containing mud increases, its sound velocity value increases, the sound duration value decreases, the amplitude changes are dispersed, and the frequency value increases. Specifically, with the increase of concrete age and when is between 0 and 10%, the changes in concrete sound velocity and sound time are minimal; With the increase of concrete age and when exceeds 20%, the frequency value significantly increases; The changes in amplitude values are similar during the age of concrete from 7 to 28 days. The measured parameters indicate that an increase in the mud content of concrete will lead to a decrease in its compressive strength, a decrease in sound velocity, an increase in sound duration, a decrease in amplitude, and a decrease in frequency. This law is highly consistent with theoretical deductions. Specifically, as increases, there is a non-linear relationship between compressive strength and (R²=0.97); When is greater than 10%, the sound velocity and sound time values change significantly, and both show linear and nonlinear relationships with the mud content; As increases, the amplitude also exhibits a nonlinear relationship with (R²=0.91);When is greater than 20%, the frequency value changes significantly and shows a linear relationship with (R²=0.95).In addition, concrete with higher mud content has a longer first wave period, larger waveform spacing, and faster signal attenuation.

Effect of Nb Alloying and Solution Treatment on the Mechanical Properties of Cold-Rolled Fe-Mn-Al-C Low-Density Steel

The automotive industry’s rapid expansion has made the development of lightweight, high-strength automotive steels essential for both energy efficiency and emission reduction. Among these materials, Fe-Mn-Al-C steel has drawn considerable interest due to its favorable combination of low density and high strength. This research examines the impact of Nb alloying (with Nb content of 0% and 0.5%) and solution treatment on the microstructure and mechanical properties of cold-rolled Fe-28Mn-10Al-C low-density steel. Various methods were employed, including Thermo-Calc thermodynamic simulations, the Olson–Cohen model, X-ray diffraction (XRD), metallographic microscopy, room-temperature tensile testing, and scanning electron microscopy (SEM). The findings demonstrate that Nb alloying significantly refines the austenite grain structure of the Fe-28Mn-10Al-C steel, improving both strength and ductility in comparison to the 0Nb steel. After solution treatment at 1050 °C for 30 min, the cold-rolling-induced defects are effectively removed, leading to a substantial increase in elongation at fracture (38.14–44.45%) and an ultimate tensile strength exceeding 900 MPa. As the solution treatment temperature increases, the austenite grains coarsen, and the number of twins increases, while yield strength and ultimate tensile strength decrease. However, there is a notable enhancement in ductility, with the material exhibiting a ductile fracture mechanism. These results offer valuable insights and a theoretical foundation for further improving the mechanical properties of Fe-Mn-Al-C low-density steels.

Meta Analysis on the Increase of Malnutrition and Sarcopenia in Older Adults

Between 20% and 50% of patients admitted to hospitals are affected by malnutrition. In a hospital setting, malnutrition can be caused by iatrogenic factors, obstacles to nutrient intake, and the complex physiological and metabolic changes that occur during the acute inflammatory response. These changes disrupt the body's natural process of utilizing nutrients, leading to hypermetabolism and/or catabolism. Sarcopenia is thought to be common in the elderly, particularly those living in nursing homes or hospitals. The decrease of physical function, muscle mass, and muscle strength is known as sarcopenia. In terms of malnutrition and sarcopenia among older adult hospital inpatients, an extensive overview of the corpus of recent research is provided by this review. It also outlines the challenges that can be overcome to improve nutrition assistance across care episodes.The objective is to assess the occurrence of malnourishment and sarcopenia in senior hospital patients, we examined 31 research publications. Using test findings for body composition, BMI, hypertension, handgrip strength, the Chair Stand Test, and handgrip strength, the effects of malnutrition and sarcopenia were examined in inpatient older individuals over the age of 60.The study of malnutrition and sarcopenia consequences among hospital inpatients involved a total of 14256 older adult participants. The analysis reveals that among hospitalised Elderly patients over 60, The frequency of sarcopenia was 26.7% and malnutrition was 28.6%. Elderly persons with malnutritional effects had greater rates of sarcopenia, suggesting that malnutrition was a significant cause to sarcopenia.

Potential Degradation of Low- and High-Density Polyethylene Films by Ochrobactrum intermedium SA1 from Sewage Sludge.

Accumulation of plastic waste is an alarming environmental concern across globe. For which, microbial degradation offers an efficient ecofriendly solution. Thus, the present study focuses on the exploration of new bacterium that can grow on and utilize polyethylene. Ochrobactrum intermedium SA1 isolated from sewage sludge (Jaipur, India) was characterized and evaluated for growth on both thermally pre-treated and untreated low-density polyethylene (LDPE) and high-density polyethylene (HDPE) films in synthetic medium at 35°C and pH 6.5 for 30 days. The bacterium was grown successfully on the polyethylene films such that 3.458 ± 0.373% and 1.586 ± 0.142% gravimetric weight loss was observed for LDPE and HDPE films, respectively. Further, LDPE and HDPE films showed highest decrease in tensile strength of 126.67% and 75.62%, respectively which was corelated with atomic force microscopy analysis depicting the increase in surface roughness after incubation with the bacterial isolate. Therefore, we believe that more detailed studies will establish Ochrobactrum intermedium SA1 as a potential tool in clearing the global burden of plastics.

Biorenewable and Circular Multifunctional Composite Polyester Based on Multi‐Scale, Multi‐Dimensional, and Multi‐Component Design

AbstractBio‐based polyethylene furandicarboxylate (PEF) plays a vital role in high‐performance packaging material for plastic replacement. However, the poor toughness blocks its practical applications. Copolymerization modification can enhance the toughness of PEF but inevitably causes a decrease in strength and barrier properties. Although nanofillers can enhance the overall performance of PEF, the intrinsic incompatibility between inert inorganic nanomaterials and PEF leads to poor reinforcement effects. Herein, a polydopamine (PDA) nanosheets/poly(ethylene‐co‐1,4‐cyclohexanedimethylene 2,5‐furandicarboxylate) (PECF) (denoted as PDAP) composite polyester is developed through the regulation of molecular and interface structures. The strategy realizes the in situ entanglement of nanofillers with the PECF chain segments through interface hydrogen bonding. The structure enhancement by molecular copolymerization and the interface enhancement by reinforcements promote crystallization, orientation, and bridging of composite systems, respectively. Benefiting from this multi‐scale, multi‐dimensional, and multi‐component synergistical design, the resultant PDAP integrates high strength (85 MPa), high toughness (111%), and excellent gas barrier properties (i.e., O2 0.016 barrer, CO2 0.013 barrer, and H2O 1.4×10−14 g cm cm−2 sPa) that are much higher than bio‐based materials and most engineering plastics. Interestingly, such the PDAP also shows superior physical recyclable, UV‐shielding, and solvent‐resistant properties, making it promising competitive for plastic replacement for high‐performance and multifunctional packaging materials.

Enhanced Properties of Cryptomeria japonica (Thunb ex L.f.) D.Don from the Azores Through Heat-Treatment

This study evaluates the chemical, physical, mechanical, and biological properties of untreated and heat-treated Cryptomeria japonica (Thunb ex L.f.) D.Don wood from the Azores, Portugal. Heat treatment was performed at 212 °C for 2 h following the Thermo-D class protocol. Chemical analysis revealed an increase in ethanol soluble extractives and lignin content after heat treatment, attributed to hemicellulose degradation and condensation reactions. Dimensional stability improved significantly, as indicated by reduced swelling coefficients and higher anti-swelling efficiency (ASE), particularly in the tangential direction. Heat-treated wood demonstrated reduced water absorption and swelling, enhancing its suitability for applications requiring dimensional stability. Mechanical tests showed a decrease in bending strength by 19.6% but an increase in the modulus of elasticity (MOE) by 49%, reflecting changes in the wood’s structural integrity. Surface analysis revealed significant color changes, with darkening, reddening, and yellowing, aligning with trends observed in other heat-treated woods. Biological durability tests indicated that both untreated and treated samples were susceptible to subterranean termite attack, although heat-treated wood exhibited a higher termite mortality rate, suggesting potential long-term advantages. This study highlights the impact of heat treatment on Cryptomeria japonica wood, emphasizing its potential for enhanced stability and durability in various applications.

Non-equilibrium solidification of Fe–B eutectic alloys under electric current pulse

This paper aims to explore the effects of electric current pulse (ECP) on the formed microstructure in Fe–B eutectic alloys. ECP treatment can change the microstructure morphology and phase composition of the Fe–B eutectic alloys from regular eutectic under conventional solidification conditions to (α-Fe) + interdendritic irregular eutectic structure. The results demonstrate that there is a maximum value of the peak current, when the maximum value is not reached, the peak current increases; the α-Fe refinement effect is obvious, the volume fraction of α-Fe increases. When the maximum value is surpassed, the α-Fe grain size increases, the volume fraction of α-Fe decreases. The phenomenon can be explained by the cluster theory for liquid metals and the non-equilibrium diffusion theory. The solidification path of Fe–B eutectic alloys under different peak ECPs was drawn, and the formation mechanism of irregular eutectic under different conditions was explained. The results of the soft magnetic properties experiments show that the morphology of the Fe2B phase and its degree of granulation have a great influence on the magnetic properties. As the size of Fe2B phase increases, the coercivity Hc increases. As the grain size of Fe2B decreases, the coercivity and residual magnetic field strength decrease.

Multiscale study on the compressive performance of diverse solid waste backfill bodies

To create green, low-energy self-compacting backfill materials, this study utilizes aeolian sand, slag, red mud, and calcium carbide slag to prepare diverse solid waste backfill materials in synergy. Additionally, a suitable amount of polypropylene fibers is added to enhance its toughness. During the experimental process, unconfined compressive strength tests were conducted using digital speckle technique. Computerized tomography scanning technology was employed for internal 3D visualization of the samples. Material strength difference mechanisms were characterized using SEM–EDS and XRD microscopic techniques. Finally, discrete element numerical simulation was utilized for analyzing the evolution of sample failure. The results show that with the increase in calcium carbide slag doping, the specimen UCS increases and then decreases, and when the doping of calcium carbide slag is 14%, the specimen UCS reaches a local maximum of 3.552 MPa; with the increase in the water–solid ratio, the specimen UCS gradually decreases, and when the water–solid ratio is 0.3, the specimen UCS reaches a local minimum of 3.26 MPa. With the increase in calcium slag doping, the mass percentage of calcium element and calcium-silicon ratio in the multi-solid waste matrix first increased and then decreased, and the micro-morphology of the multi-solid waste matrix included lamellar, block, and rod structures; With the increase in the water–solid ratio, the micro-morphology of the multi-solid waste matrix was gradually transformed, and the pore defects between the cementitious materials gradually increased. With the increase in calcium carbide slag doping, the porosity within the unit decreases, and when the doping of calcium carbide slag exceeds 14%, the porosity increases and the compressive strength decreases; with the gradual increase in the water–solid ratio, the porosity within the unit gradually increases, and the number of holes in the specimen reaches a minimum of 208 within the range of the study when the water–solid ratio is 0.24. Digital speckle technique and PFC numerical simulation together elucidate the sample’s failure process and crack evolution mechanism. Initially, the internal voids of the sample are gradually compacted, and crack propagation is slow. As the load increases to the peak, localized deformation and macroscopic crack formation occur in the sample. After the peak load, the sample exhibits significant displacement deformation, and the number of cracks increases significantly. The research findings can provide reference for the design and construction of solid waste backfill pipelines and trenches.

A multifrequency study of sub-parsec jets with the Event Horizon Telescope

The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230,GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including the main science targets, Sgr,A* and M,87, and various calibrators. Sixteen sources were AGN. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-K"onigl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL,Lac, J0132--1654, J0006--0623, CTA,102, and 3C,454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2-86,GHz range. Combining these data into a multifrequency EHT+ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor δ ∝ r^ ≤0.5 . This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius B ∝ r^ hinting at jet acceleration or efficient magnetic energy dissipation.

Effect of Water Immersion and Freeze-Thaw Cycles on Pull-off Strength of FRP Epoxy Bonded on Concrete: An experimental study

The durability and performance of Fiber Reinforced Polymer (FRP) composites for strengthening reinforced concrete structures under various environmental conditions are critical for their long-term efficacy. This study investigates the effects of water immersion and freeze-thaw cycles on the pull-off strength of epoxy-bonded FRP concrete slabs, simulating conditions typical for waterfront structures such as piles, beams, and decks. Concrete slabs, fabricated to EN 1766 standards, were reinforced with Basalt (BFRP), Glass (GFRP), and Carbon Fiber Reinforced Polymer (CFRP) sheets using Duratek® AV21 epoxy resin. The samples were conditioned in a controlled laboratory environment (23±2°C, 50±5% RH) for 24 hours before being subjected to water immersion and freeze-thaw cycling tests. Pull-off tests, conducted per EN 1542, revealed cohesive failures in the concrete substrate. The average pull-off strength for the control samples was 3.26 N/mm² for concrete and 3.97 N/mm² for epoxy resin. Water immersion results showed a slight decrease in pull-off strength for CFRP and GFRP, by 9% and 2% respectively, while BFRP exhibited a 14% increase. Freeze-thaw cycling led to increased pull-off strength across all FRP types: 7% for GFRP, 7.3% for BFRP, and 3.75% for CFRP. The findings indicate that water immersion and freeze-thaw conditions have a marginal impact on the pull-off strength of FRP-reinforced concrete. Despite the environmental exposure, all test results remained above the required pull-off strength of 2.5 MPa, demonstrating the robustness of the FRP-concrete bond. The study supports the use of FRP composites for structural reinforcement in harsh environments, highlighting their resilience under adverse conditions. Further research is recommended to explore long-term performance and additional environmental factors to ensure comprehensive durability assessments of FRP-reinforced systems.

Mechanical properties and macro–micro failure mechanisms of granite under thermal treatment and inclination

The coupling effects of inclination angle (θ) and high temperature (T) on rock degradation present significant construction challenges for underground engineering projects, such as underground coal gasification, inclined mining pillars, and nuclear waste repositories. This study is built on a novel combined compression and shear test system, investigating granite’s physical and mechanical properties and macroscopic failure characteristics under varying temperatures and inclination angles. Additionally, acoustic emission technology was used to analyze the impact of inclination and temperature on the micro-failure behavior of the specimens. The experimental results indicate that as the inclination angle increases, the specimens’ peak compressive strength and elastic modulus decrease linearly. In contrast, the shear stress increases non-linearly, suggesting that additional shear stress accelerates the initiation and propagation of cracks. Furthermore, these mechanical parameters initially increase with rising temperatures before decreasing, with a temperature threshold identified at 400 °C. The effect of inclination angle on the failure mode of the specimens is more pronounced than that of temperature; as the inclination angle increases, the failure mode transitions from splitting failure to shear failure at any given temperature. Acoustic emission results reveal that the specimens’ microcrack initiation (CI) and damage (CD) thresholds reduce with increasing inclination, while the corresponding shear stress increases. As temperature rises, the CI and CD thresholds exhibit an initial increase attended by a decrease. Finally, founded on the experimental findings, a multivariate equation was established to accurately predict the peak compressive strength and elastic modulus about θ and T. The results of this study provide valuable insights and references for the construction of underground thermal engineering under complex conditions.