As one of the most fundamental and widely applied methods for evaluating the mechanical properties of metallic materials, hardness testing plays a critical role in material development, process control, and quality assessment. The Sub-committee on Hardness Testing under Technical Committee on Metal Mechanical Testing of the International Organization for Standardization(ISO/TC164/SC3), as the primary body for international hardness testing standardization, has established a complete standard system covering the hardness testing of Brinell, Vickers, Rockwell, Knoop and Leeb, and instrumented indentation testing, while continuously improving international rules on uncertainty evaluation, traceability of reference blocks, and verification of testing machines. In parallel, Working Group of Hardness established by Quality and Related Quantities Advisory Committee under International Bureau of Weights and Measures (BIPM/CCM-WGH) ensures the global uniformity and mutual recognition of hardness values at the level of metrology through international comparisons and uncertainty specifications. In China, the standardization system in this field is mainly composed of Mechanics and Process Performance Test Methods sub-technical committee under National Steel Standardization Technical Committee of Standardization Administration of the People's Republic of China(SAC/TC183/SC4), National Testing Machine Standardization Technical Committee (SAC/TC122), and the National Force Value Hardness Gravity Metrolog Technical Committee (MTC7). It is responsible for the formulation and revision of method standards and equipment standards, as well as undertaking tasks related to metrological traceability and international cooperation. In recent years, Chinese experts have significantly enhanced their voice in international standardization work for hardness tests, leading the formulation and revision of several key ISO standards, making international standards more in line with domestic needs. Overall, the future development trend of hardness test standardization includes further standardization of traditional methods, expansion of new indentation methods, and advancement of extreme environment testing methods, providing a more solid foundation for advanced manufacturing and engineering applications.

Taking the new generation of high-strength and toughness XCrMo series oil casing pipes as an example, the relevant experimental research based on the instrumented indentation technology(IIT) was conducted to solve the technical problem that it was difficult to evaluate their fracture toughness by index of KIC with the in-situ non-destructive analysis method and the latest issued national standards. For the three types of high-strength and toughness oil casing pipes with API grades of 125ksi, 140ksi and 165ksi, the tensile properties and fracture toughness K_JC data converted by J-integral were obtained through conventional tests as references. Meanwhile, the indentation tensile properties (yield strength, tensile strength, etc.) and fracture toughness of the materials were sensed by instrumented indentation technology based on the Oliver-Pharr-Tabor multiple decoupling correction model and Energy Release Rate (ERR) model. The results showed that the overall relative deviations between the tensile properties and fracture toughness sensed by instrumented indentation technology and those from conventional tests could be controlled within 5% and 10% respectively, with high accuracy.This will provide broad application prospects for the non-destructive characterization and service evaluation of ultra-high-strength and toughness steel materials.

When conducting the test of the critical stress intensity factor for Type Ⅰ cracks(KIC) on metal materials according to the fracture toughness testing standard, the problem that the ligament size or the ratio of the maximum load to the condition load (Pmax/P_Q) fails to meet the determination conditions leads to invalid test results.5083 aluminum alloy plates were selected as the research subject, and the experiments were conducted on plane-sided specimens and side-grooved specimens with different thicknesses. Then,the influence of the side groove on KIC test results was discussed with the finite element calculation method. The results showed that the Pmax/P_Q of the side-grooved specimen was lower than that of the plane-sided specimen, and the valid KIC of the side-grooved specimens with different thickness could be both obtained. For the straight crack the side groove depth with 10% of the specimen thickness could achieve better effect on increasing the consistency of stress distribution at crack tip. Even if the initial crack size met the standard requirements, the decrease of the flatness of crack would still lead to a larger test result of KIC. Processing the side groove for the specimen first could increase the flatness of the initial crack, and was conducive to obtaining more accurate KIC test results.

1J85 Fe-Ni alloy is a soft magnetic material with excellent performance and wide applications. In some cases, it needs to be used as a high-temperature structural component, but there are few reports on the mechanical properties of its high-temperature deformation behavior. For this reason, the high-temperature tensile properties of 1J85 Fe-Ni alloy was investigated, and the structure evolution and fracture mechanism during high-temperature deformation was analyzed. The research results indicated that 1J85 Fe-Ni alloy exhibited low yield ratio, high uniform elongation, and high plasticity at room temperature. Both the strength and plasticity of 1J85 Fe-Ni alloy decreased with the increase of deformation temperature. From room temperature to 400 ℃, the decrease in plasticity was minimal. A significant decline began above 500 ℃, and a sharp drop occurred between 600 ℃ and 700 ℃. With increasing temperature, the fracture morphology changed from dimple fracture to intergranular brittle fracture. From room temperature to high temperature, the mechanical properties of 1J85 Fe-Ni alloy were influenced by both grain boundary strength and high-temperature microstructural softening (facilitated dislocation movement). With the temperature increase, material softening led to a decrease in strength while also promoting plastic deformation capability. On the other hand, grain boundary weakening reduced the plastic deformation capacity of material. During high-temperature deformation, both material softening and grain boundary weakening simultaneously affected the plastic deformation capability.

To clarify the high-cycle fatigue behavior of ZL205A aluminum alloy casing of the main reducer of helicopter and the failure mechanism of micro-porosity, the high-cycle fatigue experiments were carried out with a cycle base of 10⁷ of symmetrical cycles (stress ratio of R=-1) by up-down method. The fracture surface and porosity defects were analyzed by scanning electron microscope (SEM) and optical microscope (OM). The results showed that the median fatigue limit of ZL205A aluminum alloy at room temperature was 81.9 MPa; the fatigue cracks all initiated from the surface micro-porosity, the porosity area percentage (f) increased from 0.14% to 0.32%, the crack propagation life decreased by 52%; the porosity shortened the life through the mechanism of stress concentration-accumulation of plastic strain-rapid propagation. This study provides a key basis for life prediction and process optimization of the casing.

X65 pipeline steel is one of the primary materials used in hydrogen-blended natural gas transmission pipelines. The hydrogen embrittlement susceptibility of thermo-mechanically rolled X65 pipeline steel plate was investigated through slow strain rate tensile tests under in-situ high-pressure hydrogen environment. High-pressure hydrogen significantly degraded the plasticity of X65 pipeline steel with elongation after fracture and reduction of area decreasing by 37.4%-57.7% and 49.9%-86.3%, respectively. While the lower yield strength and tensile strength showed little change. It was revealed by fracture surfaces that the test specimens in high-pressure nitrogen exhibited typical ductile fracture, whereas those under high-pressure hydrogen showed brittle cleavage fracture initiated and propagated from deformed grain bands. These bands acted as fast diffusion channels and strong traps for hydrogen, promoting local hydrogen accumulation and facilitating hydrogen-induced cracking. Thus, it was deemed as a detrimental microstructure for the hydrogen embrittlement resistance of X65 pipeline steel.

7N01 aluminum alloy sheets rolled in two different batches were investigated systematacially. Optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM), and electron backscatter diffraction(EBSD) were employed to characterize their microstructural features at different scales. The corrosion resistance of the different sheets were evaluated through exfoliation corrosion and intergranular corrosion tests, while the mechanical properties of the two types of sheets along different orientations were obtained via tensile tests. The correlation between the microstructure and properties of 7N01 aluminum alloy was clarified. The effects of microstructural characteristics (such as phase distribution, grain morphology, and preferred orientation) of the different sheets on tensile properties, exfoliation corrosion performance, and intergranular corrosion performance were investigated. It was found that the distribution of precipitated phases and grain boundary composition were important factors affecting corrosion resistance, and the mechanical properties in different directions were closely related to crystallographic preferred orientation. Furthermore, a comparative analysis was performed on the anisotropy index and yield-strength ratio of the two batches of aluminum alloy, providing guidance for their engineering applications.

Accurately evaluating the service performance of high-strength elastic copper alloys lies in understanding their high-temperature stress relaxation behavior, and the core difficulty in this regard is the precise measurement of bending stress under high temperatures. According to the demands of ASTM E328-21 of Standard tests methods for stress relaxation tests for materials and structures, the testing equipment for bending stress relaxation of copper alloys at elevated temperature had been designed and manufactured. Subsequently, a stress measurement method for stress relaxation of copper alloys had been proposed. The copper alloy specimen was set by fixture and pressure load was applied by a press rod to simulate cantilever bending condition. A tubular furnace was used to provide a high-temperature environment. The bending stress evolution during the stress relaxation process of the copper alloy were measured and recorded by force transducer. The bending stress relaxation tests of Cu-Ti alloys were conducted at 300, 375, and 450 ℃, respectively. The results showed that the stress relaxation rates of Cu-Ti alloy were 15.0% and 28.7% respectively at 300 and 375 ℃ after holding the load for 100 h, and the stress relaxation rate reached 69.7% at 450 ℃ after holding the load for 16 h. The proposed equipment can automatically and accurately measure the stress during the high-temperature stress relaxation process of copper alloys, and has high practicality and promotion value.

In order to investigate and quantitatively analyze the factors influencing compression creep tests of titanium alloys, TC4 titanium alloy cylindrical specimens with varying specifications and precision levels were machined for compression creep tests. Five groups of comparative experiments were designed to obtain the creep curves of samples. The key creep result parameters were calculated and analyzed. The study revealed that the length-diameter ratio and size effect of the specimens showed no significant correlation with the compression creep behavior of TC4 titanium alloy. It indicated that the specimen size had little influence on the final creep performance results within a reasonable geometric proportion range. The flatness of both ends of the specimen had significant impact on the testing process and final creep results. Excessive flatness deviation would lead to uneven stress distribution, which had severe interference with the accuracy and repeatability of experimental data. In order to ensure the reliability of testing results, the flatness deviation should be controlled within 0.02 mm. In the comparison of platen configurations, it was found that the spherical pressure plate demonstrated better compatibility than flat pressure plate when the end flatness of specimen was not good. The spherical pressure plate could effectively compensate for flatness errors and initial misalignment within a certain range, thus improving the uniformity of stress distribution. This enabled relatively more reliable test results even when the specimen machining precision was limited. Regarding the displacement measurement, the study confirmed that increasing the number of grating scales was more advantageous for enhancing the accuracy of creep displacement measurements as well as the reliability of testing results. A multi-grating-scale layout could help eliminate the interference from minor deflection or tilting of specimens during axial displacement measurement, thereby more accurately reflecting the axial compression creep deformation.

Wind turbine gears are prone to fatigue failure under alternating loads, thus the fatigue performance research of its wind turbine gear steel 18CrNiMo7-6 has attracted much attention. The samples from the 18CrNiMo7-6 steel parts of wind turbine gears were selected as the research object in this study. The mechanical properties and microstructures were investigated, and the fatigue properties of were characterized. The main factors influencing the fatigue fracture were revealed, which provided a theoretical basis for the reliability design of key components of wind turbine gearboxes. The tensile tests were conducted to obtain the mechanical properties of the material. The rotating bending fatigue tests were performed to acquire the Smax-lg N(Smaxwas maximum bending stress;N was fatigue life) curve and fatigue limit data. Multi-scale observations of the fatigue fracture morphology were carried out using the characterization methods such as scanning electron microscope (SEM) and optical microscope (OM). Meanwhile, the in-situ detection equipment for inclusions was used for the statistical analysis of the non-metallic inclusions in the material. The results showed that the tensile strength (R_m) of gear steel 18CrNiMo7-6 was 1 180 MPa, the yield strength (Rp0.2) was 930 MPa, the average grain size was 11 μm, and the rotating bending fatigue strength (σ-1) was 473 MPa. It was found that the fatigue cracks mainly initiated from the non-metallic inclusions on the surface, and the main failure mode was mixed fracture of transgranular fracture and intergranular fracture. The average size of non-metallic inclusions in the steel was 23.15 μm, and the main types were sulfides and oxides of Mn and Al.

This study focused on the mechanical property characterization and inversion of through-silicon via (TSV) copper-filled materials in three-dimensional integrated circuits. The mechanical response of through silicon vias-copper nanoindentation (TSV-Cu) under thermal cycling loading directly affects the reliability of the packaging structure. However, the systematic analysis of its geometric size effect is still relatively lacking in the existing researches. For this purpose, in this paper, the mechanical behavior and microscopic mechanism of TSV-Cu with different diameters after high-temperature annealing were systematically studied by combining the nanoindentation experiments with finite element inversion. The results showed that both the elastic modulus and nanoindentation hardness of TSV-Cu after annealing were positively correlated with the diameter. The simulation inversion results indicated that the yield strength stabilized at 35 MPa after annealing, and the plastic behavior tended to be stable. The medium-diameter TSV-Cu (20 μm) exhibited relatively balanced mechanical properties (nanoindentation hardness of 1.62 GPa and modulus of 133.66 GPa). The microstructure analysis indicated that the medium-diameter TSV-Cu was more prone to grain coarsening and had better thermomechanical reliability. The differences in mechanical properties exhibited by TSV-Cu with different diameters could provide a certain basis for the selection and performance regulation of TSV-Cu in advanced packaging.

G54 steel is a new type of secondary-hardened ultra-high strength steel independently developed by China. It maintains extremely high yield strength while also possessing excellent comprehensive mechanical properties. However, the dynamic mechanical behavior and failure mechanism research of G54 steel under high-temperature and high strain rate conditions are still relatively insufficient. Therefore, it is of great significance to investigate its dynamic mechanical behavior under these conditions. Based on the separated Hopkinson pressure bar (SHPB) device, this paper conducted dynamic compression tests on G54 steel at temperatures of 100, 200, and 300 ℃ and strain rates of 1,000, 2,000, and 3,000 s^-1. The flow stress and plastic response laws of G54 steel were obtained under high strain rate loading. The results showed that G54 steel exhibited strain rate sensitivity and thermal softening effect during dynamic deformation: as the strain rate increased, the flow stress increased, while the load-bearing capacity of the material decreased at high temperatures. Combining the experimental data, the parameters of the Johnson-Cook (J-C) constitutive model were calibrated using the least squares method. The established model could well simulate the mechanical response of G54 steel under high-temperature and high-strain-rate conditions. The research results provided a reliable theoretical basis for revealing the dynamic deformation mechanism of G54 steel and its engineering application under extreme service conditions.

In order to explore the thermal deformation rule of X60 pipeline steel under multiple variable conditions and reveal its microstructural evolution mechanism, the Gleeble3180-GTC thermal simulation test machine was utilized to investigate the thermal deformation behavior of X60 pipeline steel under different deformation conditions (the deformation temperature ranging from 750 to 950 ℃, the strain rate ranging from 1 to 5 s^-1, and the deformation amount ranging from 10% to 30%). The thermal deformation constitutive equation of the material was established. The finite element analysis software of DEFORM-3D was employed for the simulation analysis of thermal deformation process. The evolution of material damage and dynamic recrystallization behavior under different deformation conditions were studied. The results indicated that the selection of a lower strain rate and a higher deformation temperature could avoid generating higher damage values during the thermal processing, and the recrystallization process was significantly suppressed under such conditions. Higher deformation temperature, strain rate, and deformation amount were beneficial for the occurrence and expansion of dynamic recrystallization. The grain refinement could be accelerated, thereby improving the plasticity of the steel.

In order to improve the accuracy and repeatability of J-integral calculations in three-point bending tests, a systematic method that integrated data preprocessing, difference-quotient analysis, and integration with unequal segments was proposed to address the issues of noise sensitivity and integration accuracy in conventional fitting and numerical integration approaches. The study applied the difference-quotient features to the identification of the linear region. Moreover, the unequal-segment integration was used to replace equal-segment assumption, thereby enhancing both applicability and precision of calculations. The original load-displacement data were first processed through point uniquifying, interpolation, and Gaussian filtering to eliminate the repeated points, backward points, and noise, thus ensuring a monotonic and smooth curve. The fitting range was then determined by analyzing the peaks and trends of the first-order central difference quotient. The integral calculation was performed using the unequal-segment integration method, while higher-order difference quotients were employed to estimate the integration error. The results demonstrated that the proposed method significantly improved the integration accuracy and stability while preserving the data authenticity. Moreover, it avoided the error estimation failure caused by non-monotonic data, and provided a reliable and reproducible technical route for the J-integral calculation.

In-situ observation technique of scanning electron microscope (SEM) was used during the in-situ tensile test of TC4 ELI alloy specimen. Microscopic morphology observation and collection of relevant crystallographic information were carried out simultaneously through secondary electron imaging secondary electron (SE) and electron backscatter diffraction (EBSD) imaging techniques of SEM. Consequently, the real-time analysis of the microscopic deformation of the sample was realized during loading, in order to reveal the failure mechanism of TC4 ELI alloy during the tensile process. It indicated that, the fracture form of the specimen was a micro-pore aggregation type fracture from the microstructure evolution law of TC4 ELI alloy specimen during the tensile process and the fracture morphology after fracture. During the deformation process, the internal dislocation density of TC4 ELI alloy increased, the orientation difference increased, and there were differences in the deformation ability of α and β and the crystal grain orientation, which led to the uncoordinated deformation, thereby resulting in tiny holes. As the deformation amount increased, the small pores connected with each other to form cracks and eventually led to failure.

The flexible composite pipe has the characteristics of good continuity, high tensile strength, high acid-base corrosion resistance, anti-scaling and waxing. In recent years, it has been rapidly popularized and used in domestic oil and gas fields. Linpan Oilfield Production Factory selected a water injection well to start the downhole test for the first time in October 2013. The test lasted for 8 months. During the test period, all water injection operation indexes were normal. The flexible composite pipe was taken out and its comprehensive performance was evaluated after the downhole test. The results showed that this pipe had a significant anti-scaling effect compared with the traditional metal oil pipes. The bending modulus of its inner and outer spiral armor layers was reduced to 92.66% and 87.14%, respectively. The bending strength was reduced to 84.74% and 69.18%, respectively. The tensile stiffness of the entire pipe was reduced by 9.70%, and the internal pressure stiffness was reduced by 8.39%. However, its overall tensile limit was increased by 2.54%, which could still ensure the safe operation and production of this flexible composite pipe under an internal pressure of 15 MPa and an external pressure of 5 MPa.