Stress Triaxiality Research Articles

Investigation of mechanical and ultrasonic properties of sandstone with different flaws characteristics under triaxial stress

This study investigates the impact of flaw angle and length on the mechanical properties and ultrasonic wave velocity of sandstone under triaxial stress. Sandstone specimens with different flaw angles (0°, 30°, 60°, 90°) and varying flaw lengths (10 mm, 15 mm, 20 mm, 25 mm) underwent comprehensive examination through conventional triaxial compression tests and ultrasonic monitoring systems. The experimental results indicate that flaw angle and length significantly affect the sandstone’s mechanical properties and ultrasonic velocity. As the flaw angle increases, both the peak stress and elastic modulus of sandstone demonstrate an upward trend. Conversely, increasing flaw length diminishes the sandstone’s mechanical strength and structural integrity. Particularly noteworthy is the observation that when the flaw length exceeds 20 mm, the unstable expansion of cracks significantly escalates, resulting in sandstone fracture at lower stress levels. The variation of longitudinal wave velocity reflected the failure process and crack evolution characteristics of sandstone. The wave velocity initially shows a temporary increase followed by a continuous decrease, with the turning point occurring near the crack closure stress. In contrast, the evolution of crack width is observed to follow the opposite pattern. This study provides new insights into the impact of flaw characteristics on the mechanical and ultrasonic properties of sandstone, offering valuable guidance for geological engineering design, rock stability assessment, and coal mining operations.

Characterization of compressive fracture strain based on bilinear strain paths

This study proposes the compressive fracture characterization method using bilinear strain paths: pre-tension and compression. Compressive ductile fracture exhibits extremely large strain, which has been regarded as being difficult to be measured. Large deformation under compressive loading makes the shape of a specimen barreled and changes the stress triaxiality rapidly. Due to these complicated and large strains, compressive fracture strain can be considered to be within the so-called cut-off region where no fracture occurs. In order to enable compression tests to be easier, an approach that can lower the range of fracture strain is needed. Uniaxial tensile deformation is a strain path that induces the growth of voids inside ductile materials and leads to ductility reduction. Ductile materials subjected to pre-tensile loading before compressive loading can show the premature compressive fracture. A ductile fracture model capable of predicting the cut-off region is selected for ductile fracture loci of the bilinear paths and implemented into the numerical simulation with different pre-tensile strain levels. The verification of the proposed characterization method is performed by comparing experimental data and simulation results for fractured specimen shapes and load-displacement curves.

Study on stress concentration and fatigue life of tubing with slip indentation

The indentation caused by slip on the outer wall of tubing is a significant contributor to stress concentration and, consequently, fatigue failure in the tubing string. Through an analysis of the interaction between slips and tubing, a mathematical model to predict slip-tubing interaction and slip crushing load is formulated, accounting for external pressure, internal pressure, and axial forces. On this basis, the influence factors and influence rules of slip crushing load are studied, and three-dimensional yield surface and tri-axial stress ellipse of tubing are investigated, considering different transverse load factors and design factors. To accurately forecast the fatigue life of tubing subjected to slip indentation, two models are established: one for fatigue life prediction and the other for tubing string vibration. In order to quantitatively assess the stress concentration arising from slip indentation, a finite element model of tubing featuring slip indentation is established. Finite element analysis reveals that stress concentration and non-uniformity are evident in the vicinity of slip indentation, with their severity intensifying as the indentation depth grows. The initial step in assessing fatigue life involves fatigue life tests on tubing material subjected to varying stress levels. Subsequently, a case study is conducted and the variations of wellhead pressure and axial stress are evaluated. Fatigue life analysis reveals that the fatigue life is notably sensitive to variations in stress amplitude and slip indentation depth. An increase in the magnitude of alternating stress and the depth of slip indentation will result in a significant reduction in the fatigue lifespan. The methodologies employed in this research, along with the resulting findings, offer a robust theoretical framework and a solid practical basis for forecasting and managing stress concentration and fatigue durability in tubing affected by slip indentation.

Grouting seepage characteristics in microfracture under triaxial stress conditions: Device design and experimental study

Water plugging by grouting in rock microfracture is a technical challenge in deep underground engineering. In this paper, a novel grouting test system was developed, which can simulate microfracture grouting tests under triaxial stress conditions. A specimen preparation method that can monitor the seepage and diffusion of microfine cement slurry in microfracture was also proposed. Microfracture grouting model tests were conducted on sandstone-like specimens to investigate the effects of confining pressure, roughness, and microfracture aperture on the seepage and diffusion characteristics of sandstone-like specimens. The test results show that microfine cement slurry can effectively seal the microfracture. However, when the microfracture aperture is small or the roughness is large, the slurry is easy to gather and deposit at the inlet, resulting in the phenomenon of "seepage filtration", which makes it difficult for the slurry to be injected into the microfracture. The pressure at the measuring point gradually decreases along the seepage and diffusion direction of the slurry, and the decreasing trend increases with the increase of microfracture roughness. The nonlinear relationship between the slurry volume flow rate and the hydraulic gradient can be described by Forchheimer's law. Moreover, both coefficients a and b in Forchheimer's equation show a gradual increase with increasing microfracture roughness. This study can provide a meaningful reference for the development of rock microfracture grouting technology in deep engineering.

Influence of steam curing on cyclic triaxial characteristics of recycled aggregate concrete: Experimental analysis and DEM simulation

The engineering application of steam-cured recycled aggregate concrete (often in a cyclic triaxial stress state) can not only improve the recycling efficiency of resources, but also accelerate the construction progress. In this paper, we adopt a combination of laboratory experiments, theoretical analysis and numerical simulation to study the cyclic triaxial characteristics of recycled aggregate concrete (RAC) under different curing regimes (20℃, 40℃, 60℃ and 80℃). The results indicate that as the steam curing temperature increases, the internal damage caused by high temperature continues to intensify, and the cyclic triaxial failure mode of RAC transitions from shear failure to compression failure, and its peak strength, dynamic elastic modulus, and dilatancy angle all show a downward trend. A linear prediction model is established based on the strong correlation between peak strength and steam curing temperature. As the loading cycles increase, the dynamic elastic modulus and dilatancy angle of RAC show exponential and linear downward trends respectively, and the decline rate increases with the increase of steam curing temperature, and the prediction models for dynamic elastic modulus and dilatancy angle are established based on quantitative relationships between variables. On the basis of experimental analysis results, a cyclic triaxial DEM model considering real recycled aggregates is established by introducing steam-cured damage indexes into the mesoscopic parameters, and its applicability in predicting cyclic triaxial mechanical properties of RAC under different curing regimes is verified. The research outcomes can save a lot of test cost and time consumption for developing steam-cured concrete with better performance, and have important theoretical guidance and practical significance for the wide application of steam-cured concrete.

Study on the effect of stress redistribution in different notched specimens of DD6 on the life of combined high and low cycle fatigue under high temperature

Under combined high and low cycle fatigue (CCF) loading, the multi-axial stress state induced by geometric discontinuities of different notch forms under the same stress amplitude can result in significant differences in fatigue performance of DD6 alloy. Therefore, it is of great importance to study the CCF behavior of Ni-base single-crystal alloy samples with differing notch geometries at the high temperatures. In order to obtain an approximate CCF lifespan, different stress amplitudes need to be applied to DD6 specimens with different notch forms. In this study, two kinds of notched DD6 plate specimens with [001] orientation were studied by CCF test at 760 °C, and the amplitudes of stresses were acquired under the same service life level. The effect of stress redistribution, in particular stress triaxiality, was evaluated on CCF lifetime of the DD6 specimens. A damage model with anisotropy considering stress triaxiality effect was suggested. The results indicated that the conventional stress–strain variables could not reflect the trend of CCF lifetime for different geometrical notched DD6 specimens, whereas the stress triaxiality at the CCF load peak could. A modified Basquin model was introduced for predicting CCF life according to the stress triaxiality at the peak loading. It can accurately and efficiently estimate the CCF life of two kinds of notched DD6 plate specimens, and the life prediction results fall within a scatter band of ±3 times of fatigue life.

Effect of temperature on permeability of mudstone subjected to triaxial stresses and its application

In order to prevent leakage of pyrolysed oil and gas and the release of contaminants from the top and bottom strata, it is essential to carry out a comprehensive study of the seepage behaviour of these strata under high temperature triaxial stress conditions. The findings of this study will contribute to the development of effective strategies for the containment and integrity monitoring of subsurface reservoirs and storage environments. Mudstone, serving as both the upper and lower strata, offers an effective barrier due to its inherently low permeability. In order to explore the change rule of mudstone sealing performance under high temperature triaxial stress, an air-heated low permeability rock mass air permeability measurement system is used to measure the ground stress buried 500 m deep and the temperature variation characteristics of mudstone permeability on the roof and floor of Jimsar oil shale in Xinjiang under 100 °C. It was found that the permeability of stressed mudstone decreased with the temperature rising up to 100 °C. The primary factor influencing the outcome was the thermal expansion of the mudstone. The magnitude of the drop value was contingent upon the triaxial stresses that could potentially be induced by the application of significant tensile forces, resulting in a relatively minor drop value. The average hydraulic radius of pore in the mudstone was also calculated, which also exhibited continuous reduction as heating up to 100 °C and the degree of reduction could reach 68%. The capacity, that prevent oil & gas and contaminant from moving cross strata as a barrier, would be strengthened when the mudstone strata from roof and floor experienced the temperature low than 100 °C. The barrier performance of mudstone as a pollutant migration barrier layer to gas pollutant migration during in-situ heat injection mining of oil shale was further evaluated.

The Study and Application on Ductile Fracture Criterion of Dual Phase Steels During Forming

High-strength steel exhibits complex fracture behavior due to the interplay between shear and necking mechanisms during stamping and forming processes, posing challenges to achieving the dimensional accuracy and reliability demanded for automotive body panels. Existing prediction methods often fail to simultaneously account for both tensile and shear fracture characteristics, thereby limiting their predictive accuracy under diverse stress conditions. To address this limitation, we propose a ductile fracture criterion that integrates both tensile and shear mechanisms, calibrated using a single tensile–shear test to facilitate practical engineering applications. This study investigates the fracture characteristics of DP780 dual-phase steel through numerical analysis and tensile–shear experiments. The findings establish a relationship between stress triaxiality and ultimate fracture strain across varying stress states, represented by the B–W curve. Simulations reveal distinct stress triaxiality behaviors under different loading conditions: under uniaxial tensile loading, triaxiality ranges from 0.33 to 0.6, with fracture strain decreasing monotonically as triaxiality increases. Under shear loading, triaxiality ranges from 0 to 0.33, with fracture strain increasing monotonically as triaxiality rises. Additional bending simulations validate that this criterion, along with the B–W curve, reliably predicts the fracture behavior of DP780, offering an effective tool for predicting fracture in dual-phase steels during stamping and forming processes.

Uncoupled ductile fracture criterion motivated by micromechanisms: Modeling and experiments

Ductile fracture behavior of metallic materials is significantly influenced by the stress states, especially for geometrically complex structures fabricated by laser additive manufacturing (AM) technique. This study proposes a new uncoupled ductile fracture criterion (DFC) that considers void evolution behaviors to predict the ductile fracture of AMed Ti-6Al-4V alloy. The new criterion is derived by synthetically taking into account the effects of stress triaxiality and the Lode parameter on microscopic void evolution behaviors, including void nucleation, growth, and coalescence, which eventually leads to the macroscopic ductile fracture. By comparison with the representative uncoupled ductile fracture criteria, the predictive ability of the proposed criterion for different metallic material is comprehensively discussed through a series of fracture experimental data published in the literature to verify the effectiveness and accuracy of the new criterion. The comparative studies indicate that the new uncoupled ductile fracture criterion can accurately predict fracture strain under different stress states. Particularly, the proposed micromechanism-motivated criterion demonstrates the distinguished effectiveness in predicting ductile fracture under high stress triaxiality compared to other criteria. Furthermore, fracture experiments of additively manufactured titanium alloy were conducted under various stress states to calibrate the material parameters of the proposed criterion. It can be found that the predicted fracture locus of AMed titanium alloy is more dependent on stress state and is generally lower than that of cast titanium alloy produced by traditional processing technology.

Multi-layer continuum model for adhesive FM 300-2 in end-notched flexure carbon laminate

The current investigation analyses the un-stable crack initiation of an adhesively bonded End Notched Flexure (ENF) specimen by means of a continuum damage formulation, based on the Bazant’s crack model, to reproduce accurately the load response and the fracture process zone of the adhesive. The specimen consisted of carbon fibre reinforced polymer adherends and two sheets of FM 300-2 adhesive films. The need of this implementation arose from experimental observations of normal transverse damage mechanisms at the bondline during the crack initiation. The damage model was based on a multi-layer configuration of the adhesive meso-structure that accounted for two damage activation functions in the normal and shear transverse directions. The results demonstrated the capability of the model to predict closely the force drop in the load–displacement curve of the ENF test. Different multi-layer configurations were studied following proper meso-structure simplification of the adhesive to use elastic and damage-capable layers in a correct order and thicknesses. The rise of the modelled shear strength allowed for keeping enough stored strain energy contributed to the low triaxiality stress in the bondline. Finally, the results demonstrated a significant influence of the layers modelling the knitted carrier to the local mechanisms of tensile fracture because of the normal transverse deformations. Unclassified. Based on Foreground information under EDA Contract No B.PRJ.RT.670 covering the Ad Hoc Project entitled “PATCHBOND II”.

Numerical Study on the Determination of Crack Initiation Angle, Stress Field and Stress Triaxiality at Crack Tip in a Cracked Beam of Functionally Graded Material

Numerical Study on the Determination of Crack Initiation Angle, Stress Field and Stress Triaxiality at Crack Tip in a Cracked Beam of Functionally Graded Material

Study on Creep Behaviors of GH3230 Superalloy With Side Notches or a Center Inclined Hole at 900°C and 1000°C

ABSTRACTGH3230 superalloy is one of the most promising materials for aviation engine hot components, characterized by lots of holes and prone to creep failure. To study the effect of the side notches or center inclined hole on creep behaviors of GH3230 superalloy, a series of creep experiments and numerical simulations based on Sinh creep‐damage constitutive model were conducted at 900°C and 1000°C. The influence mechanism of notch strengthening on creep life was analyzed under different notch sizes. The results show that the opposite combination of stress triaxiality and multiaxial stress caused by notches determines the creep damage and life. With the increase of the stress concentration factor, the notch strengthening factor demonstrates a trend of first increasing and then decreasing, whereas the increase in net stress is accompanied by the augmentation of notch strengthening factor under the same stress concentration factor.

Fractional Derivative-based Burger Creep Model for Soft Rocks and its Verification Using Tunnel Monitoring Results and Experimental Data

AbstractConsidering the creep behavior of soft and weak rocks is critical for analyzing the long-term stability of underground constructions. This paper introduces a novel creep constitutive model to characterize the creep behavior of rocks under uniaxial and triaxial stress states. The fractional derivative Abel dashpot was used to improve the Burger model, and a viscoplastic component was added in series with the modified Burgers model to replicate the tertiary phase of rock creep. The effectiveness of the model was verified using creep test data from various soft rocks and monitoring measurements from a tunnel excavated in heavily jointed weak rock masses. Furthermore, a sensitivity analysis was carried out to assess the impact of the model parameters on creep deformation, and a comparative study was performed to evaluate the efficacy of the suggested model in modeling the accelerated stage of rock creep compared with some existing models. The strong agreement observed between the calculated results and both the creep test data and tunnel monitoring measurements underscores the accuracy and validity of the proposed model. The comparative analysis further revealed that the proposed model offers the highest fitting efficiency for describing the tertiary stage of rock creep. These findings suggest that the model effectively captures the creep behavior of rocks and precisely represents the entire creep process.

Impact of triaxial stress state at various pavement depths on the dynamic modulus of asphalt mixture

The mechanical characteristics of asphalt mixture are closely related with its stress state, temperature, and loading rate, therefore, the loading condition of the asphalt mixture's dynamic modulus test should be consistent with the actual temperature, loading frequency, and stress state that are applied to the mixture in actual pavement, thus can the test produce an objective result that can accurately reflect the actual stress-strain relationship for the asphalt mixture. However, due to limitations in the loading capacity of current dynamic modulus test equipment, the present modulus tester cannot yet set such a loading condition whose stress state is consistent with that of asphalt mixture in actual pavement. As a result, the modulus testing results of the current test may not accurately reflect the actual stress-strain characteristics of an asphalt mixture under real traffic loads. Therefore, this paper aims to figure out the impact of stress state on asphalt mixture’s dynamic modulus, and firstly conducts a numerical analysis to ascertain asphalt pavement’s triaxial stress state at different depth, then, utilizing the nonlinear elasticity theory of Soil Plasticity, proposes a theoretical model that can reflect triaxial stress state’s effect on asphalt mixture’s dynamic modulus, and then, arranges a series of triaxial dynamic modulus tests for asphalt mixture in different stress state to verify the model’s effectiveness, and meantime analyzes stress state’s influencing rule to asphalt mixture’s dynamic modulus. Their results indicate, the asphalt mixture of the actual pavement is in an obvious triaxial stress state, and that the higher the triaxial stress state, the larger the dynamic modulus, particularly for the mixture near the surface, whose high stress state will lead to their dynamic modulus to be significantly larger than that of the underlying course, while the model proposed in this paper can to a large extent reflect this impact.

Mechanism of Subsurface Deformation Transmission and Geomechanical Response Inversion in Carbon Capture and Storage Project: Integrating Small Baseline Subset-Interferometric Synthetic Aperture Radar, Mechanical Experiments, and Numerical Simulation

Summary In the context of carbon capture and storage (CCS) engineering, ensuring the stability of the caprock is paramount to mitigating CO2 leakage, thus constituting a pivotal engineering challenge in CO2 geological sequestration. With the injection of CO2, pore pressure accumulates within the reservoir, bringing forth risks including diminished effective stress within the formation, surface deformation, occurrence of microseismic events, and potential caprock failure. Therefore, it is necessary to explore the geomechanical issues in CCS projects. This study focuses on the Daqingzijing in the Jilin Oilfield as the study area, utilizing the small baseline subset (SBAS)-interferometric synthetic aperture radar (InSAR) method to conduct a deformation time-series analysis in the well group area under injection and production conditions. The results reveal variations in deformation sensitivity among the sites, with surface displacements correlated to fluid injection and production, demonstrating temporal delays. At the H79 North block, the time effect is relatively minimal, with rapid propagation of formation deformation. Surface displacement in the H46 block appeared 4 months later than behind cumulative fluid volume changes. By conducting triaxial creep tests on shallow mudstone samples from the Songliao Basin under various triaxial stress states, a constitutive creep equation for caprock rocks was obtained. The numerical models of elastic and creep constitutive equations were established. The results show that the creep model exhibits superior accuracy by comparing with InSAR monitoring data (the root mean square error values of elastic and creep constitutive geomechanical models were 6.7 mm and 1.7 mm, respectively). Additionally, based on the experimental and simulation results, this study explores the transfer mechanisms of formation deformation and the inverse relationship between deformation and pore pressure. This study provides theoretical support for the geomechanical safety analysis in corresponding CCS projects.

Experimental investigation on fracture propagation in shale fractured by high-temperature carbon dioxide

The productivity of shale reservoirs was significantly enhanced by the high-temperature CO2 fracturing technique. The injection of high-temperature CO2 into the formation induced rock fracture propagation, creating advantageous pathways for fluid flow. In this research, a self-developed in situ high-temperature convective heat simulation experimental apparatus was employed to systematically conduct simulated experiments on high-temperature CO2 fractured shale under different influencing factors. The experimental results demonstrated that the permeability of CO2 increased as the injection temperature increased. The rock fracture pressure was effectively reduced by high-temperature CO2 fractured shale. Higher complexity was observed in fracture propagation, accompanied by a substantial increase in microcracks and branching fractures. The shale fracture pressure increased with increasing triaxial stress and CO2 injection rate. The confining pressure restricted the further propagation of fractures under relatively high stress conditions, thereby reducing the width and density of fractures, lowering the fracture complexity. Nevertheless, the thermal shock effect of the fluid was exacerbated as the injection rate of high-temperature CO2 increased. The initiation of microcracks was facilitated by the intensification of local thermal stress in shale, inducing multiple curved fractures and forming a more complex fracture network. Compared to horizontal bedding shale, the fracture pressure of vertical bedding shale was relatively higher during high-temperature CO2 fracturing. In addition, the geometric morphology of fracture propagation was more complex, characterized by rougher fracture surfaces, leading to a greater improvement in reservoir reconstruction volume. This research contributed to the optimization of CO2 resource utilization, provided experimental evidence for the application of high-temperature convection fracturing technology in in situ shale conversion projects.

Radiation and thermal embrittlement of RPV steels: the links of embrittlement mechanisms, fracture modes and microcrack nucleation and propagation properties. Part 1. Strategy, program and methods of experimental and numerical studies

Further development of local approach models is considered from viewpoint of links of local brittle fracture properties with embrittlement mechanisms and fracture modes for RPV steels. Strategy and program of experimental and numerical investigations have been developed that allows one to find how various embrittlement mechanisms and fracture modes are connected with the conditions of nucleation and propagation of microcracks resulting in brittle fracture of RPV steels. The experimental and numerical investigations are performed for 2Cr-Ni-Mo-V steel and A533 steel used for RPVs of WWER and PWR types. RPV steels are studied in the following states: (1) initial (as-produced); (2) thermally embrittled by a hardening mechanism; (3) thermally embrittled by a non-hardening mechanism; 4) irradiated. Experimental studies include testing specimens of different geometry (smooth and notched round bars, and cracked compact tension specimens), which allows us to obtain characteristics of brittle fracture under various stress triaxialities. Numerical studies performed with the probabilistic brittle fracture model Prometey aim to obtain the brittle fracture properties on micro- and macroscales for all the investigated states of the materials.Part 1 of the paper presents information concerning the investigated materials, the used procedures and methods. Part 2 gives the test results of smooth round bars of the investigated materials in various states and the stress-strain curves determined over wide temperature range. The experimental results for various specimens from the investigated steels in various states are represented and compared with the results predicted with the Prometey model in Part 3.

A comparative study of three types of strength criteria for rocks

Currently, the unified strength criterion (USC), the three-dimensional Hoek-Brown (3D H-B) criterion and the generalized unified strength theory (GUST) are the three types of typical rock strength criteria. In this paper, a comparative study of the three types of strength criteria is performed for rocks. Based on the nonlinear characteristics of rock strength on meridian and deviatoric planes, the USC can predict rock strength under triaxial stress state. The USC is composed of two failure functions on meridian and deviatoric planes. The failure surface of the USC in principal stress space satisfies smoothness and convexity. The predicted strength for five types of rock under the true triaxial tests were compared among the USC, the GUST, and the 3D H-B criterion. The results indicate that the USC can effectively reflect the influence of the intermediate principal stress on rock strength and accurately predict rock strength under both triaxial tension (σ1=σ2>σ3) and triaxial compression (σ1>σ2=σ3). Additionally, the conventional triaxial tests were conducted on other eight types of rock to measure the strength on meridian plane. The predicted strengths for the eight types of rock on meridian plane were compared between the USC and the original H-B, which suggests that the USC is suitable for various types of rock and provides higher accuracy.

Four-parameter punching theory for reinforced concrete flat slabs without transverse reinforcement

Despite extensive scientific research, the underlying physical principles in theoretical models for understanding punching behavior remain a concern. In this paper, a four-parameter punching theory for reinforced concrete flat slabs without transverse reinforcement has been introduced and validated. The kinematic behavior of the slab was characterized by three key parameters, i.e., critical shear crack inclination, slab rotation, and slab translation. Four distinct shear transfer effects from aggregate interlocking, concrete residual tensile stress, reinforcement dowel action, and the shear-compression ring, were considered and quantified using a novel algorithm based on these three parameters, and the fourth parameter, i.e., the direction of the minimum principal stress within the shear-compression ring. The punching capacity was subsequently determined by summing the contributions from these effects. This model was evaluated through extensive comparisons with experimental data, demonstrating that it accurately captures the influence of various parameters. Across the collected 260 test data, the average ratio of experimental to predicted punching capacity was 1.01, with a coefficient of variance of 0.11 and a coefficient of determination of 0.97. The average ratio, coefficient of variation, and coefficient of determination improved by 8 %, 21 %, and 1 %, compared to the optimal results from other design and theoretical models. The developed model can also assess all shear contributions, slab deformation, and critical shear crack inclination. It is ultimately confirmed that the proposed model can elucidate the physical phenomena and underlying mechanisms involved in punching behavior. Slab deformation primarily arises from flexural deformation, whereas shear forces are predominantly transmitted through the shear-compression ring. Punching failure is attributed to the failure of the shear-compression ring under tension-compression-compression triaxial stress.

Safety analysis of pipe string strength during transient process of ultrahigh temperature and high pressure well fracturing

AbstractWith the continuous development of deep oil and gas resources, the number of high‐temperature and high‐pressure wells is increasing, and the complexity of fracturing operations is becoming more pronounced. The safe conduct of fracturing operations is crucial for improving production efficiency. To investigate the strength and safety of fracturing strings in high‐temperature and high‐pressure wells, a transient calculation model of temperature‐pressure coupling was established for fracturing strings in high‐temperature and high‐pressure wells. The safety factor method and triaxial stress analysis were employed to evaluate the safety of fracturing strings in high‐temperature and high‐pressure wells. The method was used to assess the fracturing strings in high‐temperature and high‐pressure wells, and the effects of fracturing fluid injection rate and string size on the stress of the strings were analyzed. The results indicate that the axial force and equivalent stress at the wellhead of the fracturing string are the highest; as the fracturing time and injection rate of the fracturing fluid increase, the axial stress and equivalent stress at the wellhead of the fracturing string also increase. Small‐sized pipes are conducive to improving the safety factor of fracturing pipe string operations. The research findings can provide theoretical guidance for designing fracturing strings for high‐temperature and high‐pressure wells.