Axial Cracks Research Articles

Stress-strain relationship of airfoiled-shaped milled-cut steel fiber-reinforced concrete under uniaxial compression: Experiments and analytical model

The long-term service of concrete structures to severe environments has driven up performance requirements in terms of durability, crack resistance and toughness. Milled-cut steel fiber (MSF) holds great potential for corrosion resistance and reinforcement of concrete, benefiting from its optimized geometric and surface properties. The stress-strain relationship and damage characteristics of milled-cut steel fiber-reinforced concrete (MSFRC) under compression can serve as experimental and theoretical foundations for structural design. Thus, this study conducted compression tests on MSFRC at three different contents (Vf=0.6 %, 1 %, 1.4 %) and investigated the experimental analysis results of the full-range compressive response. Crimped steel fiber (CSF) and hooked-end steel fiber (HSF) were selected as comparison groups to confirm the effect of fiber geometry. Failure mode, toughness, and parameters characterizing the uniaxial compressive behavior of various steel fiber-reinforced concrete were experimentally assessed. The results indicate that the addition of MSF fibers increases the toughness of concrete by over 25 % compared to other types of fibers. MSF prevents the propagation of axial primary cracks and controls the maximum crack width to less than 1 mm. The negative effect of high fiber dosage on compressive strength is mitigated in MSFRC, and the optimal strength and toughness can be achieved when containing 1 % volume fraction fibers. Empirical formulas are developed to accurately predict the compressive strength and elastic modulus of MSFRC by incorporating a fiber reinforcing index (RI), with R2 value of 0.93. Furthermore, a constitutive model describing the complete stress-strain behavior under uniaxial compression has been developed for MSFRC.

Location Detection and Numerical Simulation of Guided Wave Defects in Steel Pipes

At present, researchers in the field of pipeline inspection focus on pipe wall defects while neglecting pipeline defects in special situations such as welds. This poses a threat to the safe operation of projects. In this paper, a multi-node fusion and modal projection algorithm of steel pipes based on guided wave technology is proposed. Through an ANSYS numerical simulation, research is conducted to achieve the identification, localization, and quantification of axial cracks on the surface of straight pipelines and internal cracks in circumferential welds. The propagation characteristics and vibration law of ultrasonic guided waves are theoretically solved by the semi-analytical finite element method in the pipeline. The model section is discretized in one-dimensional polar coordinates to obtain the dispersion curve of the steel pipe. The T(0,1) mode, which is modulated by the Hanning window, is selected to simulate the axial crack of the pipeline and the L(0,2) mode to simulate the crack in the weld, and the correctness of the dispersion curve is verified. The results show that the T(0,1) and L(0,2) modes are successfully excited, and they are sensitive to axial and circumferential cracks. The time–frequency diagram of wavelet transform and the time domain diagram of the crack signal of Hilbert transform are used to identify the echo signal. The first wave packet peak point and group velocity are used to locate the crack. The pure signal of the crack is extracted from the simulation data, and the variation law between the reflection coefficient and the circumferential and radial dimensions of the defect is calculated to evaluate the size of the defect. This provides a new and feasible method for steel pipe defect detection.

Fracture behavior of SiCf/SiC cladding with prefabricated cracks on the inner/outer wall

This study investigated the fracture behavior of SiCf/SiC cladding with axial cracks in the CMC layer/monolithic SiC layer on the inner and outer wall via an expanding plug test. The specimen with a prefabricated crack on the outer wall fractured in no specific direction. After the first load drop, fracture sources can be detected not only near the notch but also in other directions within the CMC layer. The simulation shows a homogeneous stress distribution resulting in a similar hoop strength to the specimen without prefabricated cracks. In contrast, the specimen with a prefabricated crack on the inner wall fractured along the notch. After the first load drop, fracture sources can be detected only near the notch. The simulation demonstrates stress concentration, resulting in a lower hoop strength. Therefore, considering the nuclear application of SiCf/SiC cladding, we are supposed to pay more attention to the defects in CMC layer in the fabrication process of SiCf/SiC cladding.

Study on the self-vibration characteristics of non-circular arches with cracks based on the transfer matrix method

As the span of reinforced concrete arch bridges continues to increase, so does the difficulty of construction. The structure is at risk of cracking. Most of the bridges under construction are non-circular arches, and there are few studies on such arches. The current study tried to investigate the self-vibration characteristics of non-circular arches with existing cracks. A computational approach proposed in the original non-circular arch is substituted with multiple infinitesimal arch segments having different radii of curvature, enabling the determination of natural frequencies and mode shapes of the non-circular arches with cracks. Furthermore, a finite element model (FEM) of the reinforced concrete structure with existing cracks is developed to assess the effects of various factors, including axial location, crack depth, and positions within the same cross-section. The results demonstrate the feasibility of the computational method using multiple infinitesimal arc segments with varied radii of curvature, yielding a maximum error of only 1.58 %, which satisfies engineering application standards. An increase in crack depth leads to a reduction in the natural frequencies of specific modes of the structure, while the effect on others is insignificant. For cracks situated at the top or bottom plates within the same cross-section, the impact differs based on the local deformation being convex or concave. If the deformation is convex, the top plate cracks exhibit a higher rate of change in natural frequencies compared to the bottom plate cracks; conversely, with concave deformation, the bottom plate cracks have a greater influence than the top plate cracks.

Triaxial compressive behaviour of ultra-high performance geopolymer concrete (UHPGC) and its applications in contact explosion and projectile impact analysis

Ultra-high performance geopolymer concrete (UHPGC) is increasingly recognised as a promising construction material in protective engineering owing to its exceptional material strength and eco-friendly characteristics. However, there is currently limited research data on the behaviour of UHPGC under complex stress states, and the applicability of some common concrete dynamic constitutive models to UHPGC requires calibration and evaluation. This paper presents an experimental study on the triaxial compression (TXC) behaviour of UHPGC under varying confining pressures with a range of 0–40 MPa. The stress-strain curves under various confinement levels and failure patterns of UHPGC are discussed. The results indicate that the peak axial stress and toughness of UHPGC increase with higher confining pressure levels, but it still exhibits noticeable softening behaviour. Under uniaxial compression, UHPGC typically fails with inclined shear and axial tensile cracks, while under TXC, particularly at confining pressures above 20 MPa, the failure mode transitions to shear failure with prominent oblique shear cracks. Additionally, existing failure criteria are calibrated to match the strength envelop of UHPGC, with the Power-law failure criterion providing the closest fitting results. Subsequently, utilising both current and pre-existing TXC data, three commonly used concrete constitutive models, including HJC, K&C and CSC, are calibrated with respect to the dominant strength parameters for UHPGC in the finite element (FE) hydrocode ANSYS/LS-DYNA. Further, numerical simulations are conducted to evaluate the effectiveness of such three calibrated concrete models in replicating the response of UHPGC panels exposed to the contact explosion or projectile impact. The simulation results demonstrate that the K&C and CSC models effectively replicate the localised damage of UHPGC panels under contact explosions, while the HJC model more accurately simulates the depth of penetration (DOP) for thick UHPGC panels under projectile impact.

Plastic Limit Pressure and Stress Intensity Factor for Cracked Elbow Containing Axial Semi-Elliptical Part-Through Crack

The aim of this study is to provide a solution for the plastic limit pressure and stress intensity factor of the elbows containing a part-through axial semi-elliptical crack by considering various crack sizes. The supporting system and loading conditions of the pipeline are described. The critical part of the observed pipeline was isolated for analysis and subjected to various sizes of semi-elliptical cracks. By performing numerical analysis, results were obtained for crack dimension ratios of c/a, and depth/thickness ratios of a/t. The obtained results include plastic limit pressure and stress intensity factor. The results were analyzed with a symbolic regression algorithm, and closed-form solutions for the limit pressure and stress intensity factor were proposed. To validate pipeline integrity, the Structural Integrity Assessment Procedure (SINTAP) was applied, and the FAD (Failure Assessment Diagram) was generated for cracks below the FAD function. The failure pressure was calculated by determining the points where the loading paths intersect the FAD function.

Mechanical behaviour and macro-micro failure mechanisms of frozen weakly cemented sandstone under different stress paths

Significant unloading failure zones in artificial freezing shaft sinking projects in western China are primarily caused by stress release. To investigate the deformation and failure mechanisms of frozen weakly cemented sandstone (FWCS), three groups of triaxial unloading tests were conducted under different initial principal stresses (σ₃ = 3, 6, and 10 MPa) with an unloading rate of 0.05 MPa/s. Scanning electron microscopy (SEM) was employed to examine the micro-fracture characteristics of the failure surfaces. The results revealed that, compared to traditional triaxial and room-temperature triaxial compression tests, the strength and plastic deformation characteristics of FWCS are significantly weakened under unloading conditions. However, lateral deformation, particularly volumetric strain, increased markedly, exhibiting pronounced dilatancy characteristics, especially along stress path III (i.e., post-peak axial stress loading with confining pressure unloading). Unloading leads to a reduction in cohesion and an increase in the internal friction angle of FWCS, with the most significant changes observed along stress path IV (i.e., pre-peak constant axial displacement loading with confining pressure unloading). Macroscopic and microscopic analyses indicate that the failure mechanism of FWCS under complex unloading stress paths is driven by the rapid accumulation of energy caused by unloading, which results in the development and propagation of axial and circumferential cracks, widespread particle breakage, and the formation of inter-granular and trans-granular fractures, as well as shear scratches at the micro level, ultimately manifesting macroscopically as shear-tensile composite failure.

Burst failure analysis of PVC-UH pipes with axial surface crack based on multiple methodologies

High-performance unplasticized polyvinyl chloride (PVC-UH) offers superior strength and performance compared to PVC, making it a common choice for municipal water supply pipelines. Cracks in PVC-UH pipes are challenging to prevent throughout the entire production and maintenance process. Precise and applicable failure assessment and residual bearing capacity calculation methodology are crucial for ensuring the safe operation and maintenance of PVC-UH municipal water supply pipes. To this end, this paper conducted material uniaxial tensile tests, fracture toughness tests, and pipe burst tests. The study determined the true stress–strain relationship, fracture toughness, burst pressure, and fracture morphology of PVC-UH pipes through testing. Failure pressures of cracked PVC-UH pipes were forecasted using different methodologies, and their accuracy and applicability were evaluated by comparing predicted values with the results of bursting tests. Two calculation methods for determining the failure pressure of pipelines with an axial outer surface crack are proposed based on plastic deformation, damage factor, and fracture mechanics theory. These proposed calculation methods are compared against current methods for determining the failure pressure of pipelines with crack defects, highlighting the higher accuracy of the methods introduced in this paper. The research results can serve as a reference for selecting failure assessment methods for PVC-UH pipelines. Additionally, the proposed calculation methods can accurately and rapidly predict the failure pressure of pipelines with identified axial surface crack sizes, providing technical support for engineering safety assessments of PVC-UH pipelines.

Study on the Stress Intensity Factor of Tilt Crack on the Inner Surface of Pipeline

Abstract Cracking is one of the key factors jeopardizing the safe operation of pipelines, and Stress Intensity Factor (SIF) is an important parameter for evaluating the degree of crack danger. Cracks on engineering pipelines often appear in irregular patterns. In this paper, with FRANC3D crack analysis software, SIFs of the circumferential tilt cracks and axial tile cracks on the inner wall surface of a pipe under internal pressure were studied with concentration on the effects of the crack tilt angles. Mode I stress intensity factor weakening effect KI/K0 was defined and influences of the crack tilt angle, pipe and crack size on KI/K0 were investigated. With enough simulation results, empirical formulas for calculating the Mode I SIF for the circumferential or axial tilt crack were obtained by modifying the formulas for calculating the SIF of the crack in AMSE FFS-1.

An experimental and theoretical investigation on residual stress of 7075-T651 aluminum alloy hole under electromagnetic cold expansion

The electromagnetic cold expansion process (ECE) was adopted in this work. The theoretical plastic radius, hole wall stress, radial stress, circumferential stress and release stress under different expansion rates (ER) were studied based on thick cylinder theory and ECE experiments. The released strain, residual stress (RS) and failure force were measured. The tensile fracture morphology was characterized. The results showed that the theoretical plastic radius (maximum 15.87 mm), internal stress (maximum 982.9 MPa), radial stress (maximum −820.9 MPa) and circumferential stress (maximum −271.4 MPa) increased with the increase of ER. The absolute radial and circumferential stress decreased and increased in negative and positive ranges respectively with distance increased. The release strain (maximum −3033 με, 10−6 microstrain), radial RS (maximum 600.9 MPa) and circumferential RS (maximum 601.1 MPa) also increased with the increase of ER, and the minimum relative error of the plastic zone radius of the theoretical model was 3.78 % proving the reliability of the model. In addition, ECE increased the release stress (the maximum radial and circumferential release stresses were 1402.6 MPa and 747.5 MPa) and decreased the failure force (minimum 44.7kN) with increased ER. The initial crack position tended to transition from the inlet and outlet surfaces to the middle position, and the crack propagation angle and axial crack size gradually decreased with the decreased ER and stress level.

Pipeline Circumferential Cracking in Near-Neutral pH Environment Under the Influence of Residual Stress: Dormancy and Crack Initiation

The purpose of this study is to identify the integrity challenges encountered by buried pipeline steels, specifically to address Circumferential Near-Neutral pH Corrosion Fatigue (C-NNpH-CF). Damage to the pipeline’s protective coating and corrosion conditions increase the risk of service failures caused by C-NNpH-CF. (Note that this mechanism has previously been termed near-neutral pH stress corrosion cracking.) Unlike axial cracking, circumferential cracking is primarily influenced by residual stress from pipeline bending, geohazards, and girth welds. External corrosion pits often lead to dormant cracks, with growth ceasing around 1 mm depth due to reduced dissolution rates. Investigating the impact of bending residual stress (an appropriate source of axial residual stress) and cyclic loading (simulated pipeline pressure fluctuation), the study employs the digital image correlation (DIC) method for stress distribution analysis. Factors like applied loading, initial notch depth, and bending conditions influence crack initiation and recovery from the dormancy stage by affecting stress distribution, stress cells, and stress concentration. Cross-sectional and fractographic images reveal time/stress-dependent mechanisms governing crack initiation, including dissolution rate and hydrogen-enhanced corrosion fatigue. The study emphasizes the role of various residual stress types and their interactions with axial cyclic loading in determining the threshold conditions for crack initiation.

Strain rate effects on fragment morphology of ceramic alumina: A synchrotron-based study

Dynamic (600–1000 s−1) and quasi-static (0.001–0.01 s−1) compression experiments are conducted on a high-purity alumina ceramic using a split Hopkinson pressure bar and a material test system, respectively. The postmortem fragments of ceramic samples at different strain rates are then characterized via synchrotron micro computed tomography (CT). The three-dimensional (3D) morphologies of fragments are quantified using the gyration tensor analysis after proper segmentation of CT images. The mean fragment size decreases in a power-law form while the mean shape indices (sphericity, elongation index and flatness index) increase in a logarithmic-linear form, with increasing strain rates. In addition, the fragment size and shape distributions are all found to follow the Weibull probability distribution. To reveal the underlying mechanisms of such strain rate effects, high-speed optical and X-ray imaging are implemented to capture the fracture process of ceramic samples under quasi-static and dynamic compression. Primary and secondary wing cracks (PWCs/SWCs) control the fracture and fragmentation of the ceramic under both loading conditions. Compared to quasi-static loading, a considerably larger number of SWCs are produced under dynamic loading, and pronounced branching and bridging occur among the PWCs, which prevent the PWCs from coalescing into axial splitting cracks. Consequently, crack networks composed of high-density wing cracks break the sample into finer and more isotropic fragments, consistent with CT characterizations. Scanning electron microscopy is utilized to analyze the micro damage modes of ceramic samples. Transgranular fracture dominates the grain-scale damage and contributes to the higher dynamic fracture resistance of the alumina under dynamic loading, as a result of more homogeneous nucleation and growth of micro cracks.

Unveiling the microscopic compression failure behavior of mesophase-pitch-based carbon fibers for improving the compressive strength of their polymer composites

Mesophase-pitch-based carbon fiber (MPCF) reinforced polymer (MPCFRP) composites show great potential for aerospace applications due to their excellent thermal conductivity and dimensional stability. However, the low compressive strength severely limits their application in high load-bearing areas. To address this issue, MPCF-A with a split-radial structure and MPCF-B with a skin-core structure were meticulously prepared by fiber structure regulation. The compression failure behavior of MPCFs at the monofilament and the microregion levels was investigated using the tensile recoil method and in-situ micropillar compression technique. MPCF-A exhibits the failure mode of petal-like lamellar separation due to axial crack penetrating along the (002) crystal plane of graphite layers, with the compressive strength of the core region (391 MPa) being higher than that of the skin region (360 MPa). Conversely, MPCF-B demonstrates a large transverse fracture in the skin region during damage, along with uniform microcracks in the core region. Notably, the compressive strength of the core region (547 MPa) significantly exceeds that of the skin region (456 MPa). Furthermore, the compressive strength of MPCF-B monofilaments (583 MPa) is higher than that of MPCF-A (462 MPa), attributed to factors such as the smaller graphite crystallite size (La = 36.54 nm, Lc = 26.75 nm), lower crystallite orientation (Z = 10.21°, R = 0.25), smaller pore size (Rg = 9.56 nm), and higher amorphous carbon content (g = 69.77%, K = 20.38). Consequently, the compressive strength of MPCFRP-B (232 MPa) is enhanced by 30.3% compared to MPCFRP-A.

Load-independent creep constraint analysis and solutions for surface cracks in pressurized pipes

Using load-independent creep constraint parameters Q* and Qm*, the variations of crack front stress field and constraint level are analyzed for various crack sizes of pipelines containing internal surface cracks under high temperature conditions. The results show that the trends of stress changes in the axial and circumferential internal surface crack front for different crack sizes are similar. For axial internal surface cracks, when the crack depth to length ratio a/c is the same, the maximum values of crack front Q* and Qm* are shifted from the deepest part of the crack (2Φ/π = 1) to the vicinity of the free surface (2Φ/π = 0.2) as the crack depth a/t increases. As for the circumferential inner surface cracks, when the crack depth a/t exceeds 0.2, the locations where the maximum values of crack fronts Q* and Qm* appear are mainly concentrated in the deepest part of the crack (2Φ/π = 1). Based on the calculation results of the constraint parameters, the empirical formulas for the engineering calculation of the relationship between the average constraint parameters (Qavg* and Qm‐avg*) and the crack size are obtained by fitting.

Interference study of double cracks on the inner surface of pipe bends with axial misalignment weld defects

In engineering practice, erosion wear cracks in pipelines occasionally exhibit a phenomenon of multiple crack aggregation. To investigate the effect of the interaction between double cracks in natural gas pipelines with axial misalignment welds, this paper, based on fracture mechanics, firstly establishes a model of an external axial misalignment weld bend. By analyzing the double-crack model of the main crack and subsidiary crack, the interference effect of the subsidiary crack on the leading edge of the main crack is studied. The results show that when both the main crack and the accessory crack are annular cracks, all the points on the leading edge of the main crack are within the shielding zone of the accessory crack under the condition of co-linear neighboring position. Meanwhile, under the condition of coaxial neighboring position, all the points on the leading edge of the main crack are partly within the shielding zone of the accessory crack and partly within the reinforcing zone. Conversely, when the main crack is an annular crack and the accessory crack is an axial crack, the conclusion is opposite to the former. This study can provide a theoretical basis for the safety evaluation of multi-cracked gas pipelines.

Study on damage characteristics and mechanisms of arch concrete slabs with outer arch side facing water under inner-arch contact explosion

The anti-explosion performance of the arch concrete slabs under different working conditions is an important subject that has been widely studied in recent years. In this study, five arch concrete slabs with 60 mm thickness and different spans (500, 550, and 600 mm) with the outer arch side facing water were tested under inner-arch contact explosion. At the same time, the controlled explosion test of the arch slab with the outer arch side facing air was also carried out. The experimental results showed that the damage mode of the arch slabs with the outer arch side facing water was mainly long axial cracks on the mid-span, blasting pit on the inner arch side and radial cracks on the outer arch side. The crack development of the control group specimen was more complete, and there was greater and deeper spalling damage on the outer arch side. Moreover, a fully coupled model of contact explosion was established based on the Lagrange–Euler coupling algorithm, and the reliability and accuracy of the model were verified by comparing with the experimental results. The propagation laws of stress waves in arch slab was then studied. The dynamic responses of arch slabs with different working conditions and spans were studied, and the damage mechanisms of arch slabs were also analyzed. The results showed that, under the same explosion load, the arch slab with the outer arch side facing water exhibited more uniform stress than the arch slab with the outer arch side facing air. And the acceleration response showed that, the arch slab with the outer arch side facing air mainly deformed along the explosion direction, but the arch slab with the outer arch side facing water not only deformed along the explosion direction but also had a rebound trend. Moreover, because of the existence of the water interface, the transmission of compression stress wave in the arch slab increased and the reflection decreased when it reached the outer arch surface.

Fracture analysis of hydrogen-embrittled API X52 pipes at low temperature

This paper quantifies the effect of temperature (ranging from room temperature (RT) to -90 °C) on fracture toughness for hydrogen-embrittled API X52 by combining small punch (SP) test data and finite element (FE) damage analysis. For the FE damage analysis, a multi-axial fracture strain damage model was used, and the parameters were determined by analyzing the tensile and SEN(T) test data in air at RT. The hydrogen-enhanced ductile fracture was considered using the hydrogen-embrittlement constant, which was determined by analyzing the SP test results in hydrogen. Due to the effect of the interaction between strength and hydrogen-induced ductility loss on fracture toughness, the predicted fracture toughness in terms of temperature does not show a monotonic decrease up to -90 °C; rather, it decreases up to -30 °C, then increases slightly before decreasing again. Fracture mechanics analysis of a hydrogen-embrittled pipe with an axial surface crack using the determined fracture toughness values showed that the maximum pressure decreased slightly (less than 9 %) with decreasing temperature up to -90 °C, suggesting that the effect of temperature on the maximum pressure would not be so significant for API X52.

Mechanical behavior of a novel compact steel-UHPC joint for hybrid girder bridges: Experimental and numerical investigation

Ultra-high-performance concrete (UHPC) has recently been applied as an alternative to normal concrete in steel-concrete composite structures. In this paper, a novel compact steel-concrete joint with UHPC grout, which utilizes shear connectors, a bearing plate and a simple I-shaped steel girder, is proposed for long-span railway hybrid girder bridges. To investigate the mechanical behavior and force transfer characteristics of the proposed compact steel-UHPC joint (CSUJ), a model test with reduced scale and push-out tests of its main force transfer components were conducted. The specimens' failure model, load-interface slip, and strain development were compared and discussed in detail. Furthermore, a finite element model of the CSUJ was established to investigate the internal damage evolution and the load transfer path. The test results indicated that the steel-UHPC joint possessed excellent axial stiffness and cracking resistance. The axial stiffness before cracking is 2.6 times that of the steel-concrete joint prototype with C60 concrete grout. Upon loading, the filled-in UHPC of the CSUJ was in elastic compression. In the ultimate limit state, the steel-UHPC joint exhibited great integrity, and the ultimate failure mode of the CSUJ was controlled by the adjacent axially loaded steel beam segment. Results of push-out tests showed that the force transfer component with perfobond leiste (PBL) connectors demonstrated greater ductility than other transfer components. In terms of the force transfer rate and uniformity, the proposed CSUJ provides desired stress distribution and force transfer behavior. The shear connectors, bearing plate, and end face of the I-girder transferred 49%, 35%, and 16% of the total axial force, respectively.

Seismic Performance of Prefabricated Reinforced Concrete Structure Beam Joints Based on the Internet of Things

Abstract Because buildings are easily damaged and collapsed by earthquake disasters, a study on the seismic performance of prefabricated reinforced concrete beam joints based on the Internet of Things has been proposed. Side joints with the largest bottom column section and the largest axial compression ratio of 100 m high prefabricated reinforced concrete structure were selected for the test. The test loading scheme is completed through the test loading device and the test loading system. An logging while drilling wave is selected as the test-simulated seismic wave, and the column axial force, hysteresis curve, displacement point, strain force, and crack position are taken as the main measurement contents. To do this, the DH-3816 data collection was completed based on the Internet of Things and the test data were recorded by DH-3816 data acquisition system. The results show that the proposed method consumes much energy and has high ductility under a low cycle reciprocating load. The bearing capacity in yield state, limit state, and failure state is better, and the degradation trend of strength and stiffness is gentler. Fuzzy optimization is used to test the viability of the proposed mechanism and the results are promising.

The method for the estimation of fracture toughness of thin-walled metallic tube considering the effect of crack orientation

Thin-walled metallic tubes are very susceptible to axial or circumferential cracks in harsh environments such as high temperature, high pressure, and severe corrosion, which seriously endangers the service safety of thin-walled tubes. Fracture toughness is an essential mechanical property index for evaluating the service safety of thin-walled metallic tubes, and its special thin-walled structure cannot be tested by using the specimens with standard configuration. In this work, based on the principle of energy density equivalence, the load–displacement and J-integral expressions of thin-walled metallic tubes with axial and circumferential cracks are proposed, and the fracture toughness test method of thin-walled metallic tubes with axial and circumferential cracks is established. Typical zircaloy cladding tubes were selected to complete the fracture test, and the influence of crack orientation on their fracture properties was investigated. The results show that the fracture toughness of circumferential cracks is lower than that of axial cracks, the circumferential cracks also face the risk of fracture failure, and the estimation of fracture properties of the cladding tubes with circumferential cracks cannot be simply replaced by axial cracks.