Correlations between the mechanical properties and surface scratch resistance of polylactic acid (PLA) are investigated via tensile and scratch tests on samples after degradation in soil for various times. The results show that the tensile yield strength of PLA is inversely proportional to the natural logarithm of the degradation time, and the scratch resistance and fracture toughness of PLA and the temperature rise near the indenter all increase and then decrease. The surface crystallinity of PLA also increases and then decreases, indicating that it and the scratch resistance are closely related. These findings provide useful information about how PLA behaves under degradation conditions. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).

Improving the fracture toughness of agricultural soil-engaging components can mitigate the detrimental effects of hard particles in the soil while maintaining the wear resistance of the components, thereby improving the service performance. The wear resistance of the parts can be improved by surface treatment, but the surface toughness after treatment still needs to be further improved. In this study, WC10Co4Cr@YSZ (Yttria Stabilized Zirconia) core-shell structured composite powder was synthesized by modifying commercial WC10Co4Cr powder using the sol-gel method, and WC10Co4Cr coatings were prepared using the powders before and after modification. The microstructure of the powder and coatings were characterized. The mechanical properties and wear resistance of the coatings were evaluated through microhardness, nanoindentation, and friction testing. The hardness of the YSZ-modified composite coating was comparable to that of the unmodified coating, yet it exhibited lower porosity and twice the fracture toughness. Wear test results indicated that the coating's wear loss was greatly reduced compared with the substrate. In addition, the wear rate of the YSZ-modified coating was 71.11 % lower than the unmodified coating, demonstrating its exceptional wear resistance. The findings show that incorporation of YSZ into the coating system further enhanced wear resistance. The strengthening mechanisms resulting from the YSZ inclusion include the pinning effect, which controls the size and distribution of the WC grains, the shell structure that prevents overheating, and the improved fracture toughness of the coating. This work provides a new way to extend the service time of agricultural soil-engaging components.

In aggressive environments, including acidic environments, low and high-plasticity clays play an important role in transmitting and spreading dangerous pollution. Stabilisation of these types of soils can improve their characteristics. In this research, different ratios of two precursors with a low calcium percentage, for example, waste statiti-ceramic sphere powder (WS-CSP) and a high calcium percentage (e.g. ground granulated blast furnace slag [GGBFS], were employed to investigate the properties of soils with different plasticity indices [PIs]). Low and high-plasticity-stabilised and stabilised with 5 wt% Portland cement specimens were prepared and exposed to an acidic solution with a pH of 2.5 in intervals of 1, 3, 6 and 9 months. The long-term durability of specimens was evaluated using the uniaxial compressive strength test (UCS) and bending strength test (BS). Additionally, the microstructures of these specimens under various time intervals were analyzed using scanning electron microscopy and Fourier-transform infrared. According to the results, in an acidic environment, the reduction in UCS, BS, toughness and secant modulus of elasticity (E50) for low-plasticity-stabilised specimens and containing 100% WS-CSP was lower than that of other specimens. The Taguchi method and ANOVA were used to investigate the effect of each control factor on the UCS and BS.

This study addresses the utility of polyelectrolytes, i.e., cationic poly(diallyldimethylammonium chloride) (PDADMAC) and anionic polystyrene sulfonate (PSS), as additives to improve properties of the polymer-stabilized soil. This paper specifically focuses on the resistance of polymer-stabilized soils to degradation and/or damage during and following multiple wetting-drying cycles (zero, one, two, three, five, and seven cycles). Each cycle consisted of 24 h of moisture conditioning using capillary rise followed by 24 h of drying. Then, these specimens were evaluated for their unconfined compressive strength (UCS). The microstructure and composition of the soils were investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray fluorescence analysis (XRF). Based on the results, the soils used in this study for polymer treatment were primarily composed of carbonates and silicates with a small amount of clay minerals. The polyelectrolyte stabilizers (PDADMAC and PSS) and polyelectrolyte complexes (PECs) were added to the soils at dosages ranging from 0.2% to 1.6% by weight of dry polymer to dry soil. Treated soils demonstrated increased UCS compared with untreated counterparts. The untreated soils exhibited rapid degradation of UCS and mechanical collapse within three to four wetting-drying cycles. On the other hand, the polymer-treated soils exhibited a strength reduction of between 10% and 50% following the first cycle and then maintained the UCS of about 3-6 MPa after completion of all wetting-drying cycles. Furthermore, the stabilized soil demonstrated significant improvement in toughness compared with their untreated and cement-treated counterparts. The ability of the polymer-stabilized soils to stand up to wetting-drying cycles is a key finding and contribution of this study.

Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation. Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production. In this study, using the well-known notched semi-circular bend (NSCB) sample and the novel double-edge notched flattened Brazilian disc (DNFBD) sample combined with a split Hopkinson pressure bar (SHPB), various dynamic anisotropic fracture properties of Lushan shale, including failure characteristics, fracture toughness, energy dissipation and crack propagation velocity, are comprehensively compared and discussed under mode I and mode II fracture scenarios. First, using a newly modified fracture criterion considering the strength anisotropy of shale, the DNFBD specimen is predicted to be a robust method for true mode II fracture of anisotropic shale rocks. Our experimental results show that the dynamic mode II fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode I fracture. The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation, while the maximal ones occur in the Divider orientation. In addition, it is interesting to find that the mode II fracture toughness anisotropy index decreases more slowly than that in the mode I fracture scenario. These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Understanding the anisotropic fracture behavior and the characteristics of the fracture process zone (FPZ) under size effects in laminated rocks, as well as its role in rock fracturing, is crucial for various engineering applications. In this study, three-point bending tests were conducted on shale specimens with varying bedding angles and sizes. The anisotropic characteristics and size effects of fracture parameters were revealed. A comparative analysis was performed on the evolutions of FPZs computed using size effect theory, digital image correlation (DIC), and linear elastic fracture mechanics. The results divulged that: (i) With increasing bedding angles, there is a noticeable decrease in apparent fracture toughness (KICA), apparent fracture energy (GICA), and nominal strength (sNu). When the bedding angle of shale is less than 45 degrees, the crack propagation and fracture parameters are mainly influenced by the matrix. Contrary, shale with bedding angles greater than 60 degrees, the crack propagation and fracture parameters are mainly controlled by the bedding. When the bedding angle is between 45 degrees and 60 degrees, the fracture propagation evolves from permeating the matrix to extending along the bedding; (ii) The fracture parameters exhibit significant size dependent behavior, as KICA and GICA rise with increasing specimen size, but sNu falls with increasing specimen sizes. The fracture parameters align with the theoretical predictions of Bazant size effect law; and (iii) The lengths of DIC-based FPZ, effective FPZ, and inelastic zone follow Wshape variations with bedding angle. The dimensionless sizes of FPZ and inelastic zone decrease with specimen size, indicating a size effect. Furthermore, there is a negative relation between KICA and the dimensionless size of the FPZ, while sNu is positively correlated to the dimensionless size of the FPZ. This highlights the essential role of the FPZ in the size effect of rock fracture. The bedding angle exerts an influence on the FPZ, subsequently affecting the anisotropic fracture and size-dependent behavior of shale. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

Rock fracture toughness is a critical parameter for optimizing reservoir stimulation during deep resource extraction. This index characterizes the in situ resistance of rocks to fracture and is affected by high temperature, in situ stress, thermal shock, and chemical corrosion, etc. This review comprehensively examines research on rock fracture properties in situ environments over the past 20 years, analyses the influences of various environmental factors on rock fracture, and draws the following conclusions: (i) Environmental factors can significantly affect rock fracture toughness through changing the internal microstructure and grain composition of rocks; (ii) While high temperature is believed to reduce the rock strength, several studies have observed an increase in rock fracture toughness with increasing temperature, particularly in the range between room temperature and 200 degrees C; (iii) In addition to a synergistic increase in fracture toughness induced by both high temperature and high in situ stress, there is still a competing effect between the increase induced by high in situ stress and the decrease induced by high temperature; (iv) Thermal shock from liquid nitrogen cooling, producing high temperature gradients, can surprisingly increase the fracture toughness of some rocks, especially at initial temperatures between room temperature and 200 degrees C; and (v) Deterioration of rock fracture toughness occurs more rapidly in acidic environments than that in alkaline environments. In addition, this review identified current research trends and suggested some potential directions to provide suggestions for deep subsurface resource extraction. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

Expansive soil, characterized by widespread fissures, is a special type of soil prone to localized fissure propagation, leading to failure and instability, often resulting in landslides. Numerous studies have applied fracture mechanics theory to analyze soil failure along fissures, but no standardized testing method has been established. This paper reviews existing soil fracture toughness testing methods, designs an integrated system combining digital image correlation(DIC) technique and electrical resistance testing, and employs the Cracked ChevronNotched Brazilian Disc (CCNBD) method to assess the fracture toughness of expansive soil. The deformation and internal damage accumulation processes of the specimens were monitored. The K & Iukcy;c and K & Iukcy;& Iukcy;c of expansive soil were tested at moisture contents of 15 %, 20 %, and 25 % using specimens with three different crack length ratios (a/R). The role of water was explored by injecting water into the fissures. The results showed that K & Iukcy;c of expansive soil ranged from 10 to 36 kPa center dot m0.5, with a linear negative correlation to moisture content and a proportional relationship to tensile strength, having a proportionality coefficient of 0.331. The K & Iukcy;& Iukcy;c ranged from 20 to 70 kPa center dot m0.5,and it is greater than K & Iukcy;c under the same conditions. Based on the load, internal damage, strain, and fissure area during the tests, the failure process of expansive soil along fissures was divided into four stages: initial deformation stage(I), quasi-elastic deformation stage(II), fissure extension stage(III), and failure stage(IV). Water injection into the fissures reduced the soil's fracture toughness, with a more significant reduction as a/R increased and the failure showed progressive behavior. The CCNBD method, combined with DIC technique and electrical resistance testing, effectively measures the fracture toughness of soil, aiding in understanding the failure mechanism along fissures and providing a basis for preventing and controlling landslides and other hazards in expansive soils.

In this study, lime soil was reinforced with preservative-treated rice straw fibers to improve its brittle behavior and overall performance. Straw fibers of varying lengths and amounts were used, and the resulting unconfined compressive strength, shear strength, and flexural strength of the reinforced soil were determined. The effect of fiber reinforcement on the mechanical properties and fracture toughness of limestone soils was determined, and the finite element (FE) software ABAQUS was used to analyze the specimen loading, crack extension, and specimen damage for developing a fracture toughness prediction model. The test results showed that the compressive strength, shear strength, and Mode I fracture toughness of soil increased with the fiber length and content. Also, a linear correlation between fracture toughness and unconfined compressive strength and shear strength was found. Therefore, the fracture toughness can be predicted by establishing a correlation equation. The disparity between the simulated fracture toughness obtained by FE analysis and that measured laboratory test is <3 %, validating the reliability and accuracy of the developed model. From the FE model analysis, crack propagation can be divided into four stages, i.e., no crack, crack appearance, crack development and expansion, and crack penetration. The friction and interlocking force between the rough texture of the fiber surface and the soil and the skeleton structure formed by the fiber in the soil can overcome the soil force. Therefore, the toughness of fiber-reinforced soil is better than that of lime soil.

To address the issue of high fracture and wear failure rates caused by the lack of toughness and abrasion resistance in the steel used for soil-engaging components of tillage machinery, a novel composite heat treatment process, normalizing and intercritical quenching and tempering (NIQT), is proposed. By regulating the austenitizing heating temperature in the intercritical area (ferrite/austenite two-phase area), the type, content, and distribution of phases in the 27MnCrB5 test sample could be precisely controlled, which further influenced the mechanical properties of the material. The results demonstrated that a multiphase composite microstructure, predominantly consisting of martensite and ferrite, could be obtained in the 27MnCrB5 steel treated by the NIQT process. The results of an EBSD test indicated that the predominant type of grain boundary following the NIQT heat treatment was a high-angle grain boundary (approximately 59.5%), which was favorable for hindering crack propagation and improving the impact toughness of the material. The results of the mechanical tests revealed that, when the quenching temperature was set to 790 degrees C, the 27MnCrB5 steel attained excellent comprehensive mechanical properties, with a tensile strength of 1654 MPa, elongation of 10.4%, impact energy of 77 J, and hardness of 530 HV30. Compared with conventional heat treatment processes for soil-engaging components, this novel process has the potential to enhance the performance of soil-engaging components and prolong their service life.