Fatigue Performance Research Articles

Experimental study on the flexural fatigue performance of slag/fly ash geopolymer concrete reinforced with modified basalt and PVA hybrid fibers

Geopolymer, owing to its inherent low-carbon emission advantages, emerges as a potential substitute to diminish reliance on high-carbon-emitting Portland cement. Nonetheless, similar to ordinary Portland cement concrete, geopolymer concrete tends to exhibit brittle fracture under cyclic bending loads. To improve its flexural fatigue performance, this paper incorporated the modified basalt (MB) fiber and PVA fiber in hybrid form into the geopolymer concrete. The flexural fatigue behavior of hybrid fibers reinforced geopolymer concrete was investigated, with a focus on the influence of varying hybrid fibers volume fractions. Digital Image Correlation technology was utilized to accurately track the evolution of crack length and the local strain field during the fatigue failure process. The results revealed that the incorporation of both MB and PVA fibers effectively delayed the initiation and propagation of cracks, leading to a more complex path of fatigue cracks. The PVA fiber demonstrated significant efficacy in inhibiting microcracks, while the MB fiber played a crucial role in controlling the expansion of macroscopic cracks. When the proportion of MB fiber was predominant in the hybrid mix, the crack development pattern mirrored that of samples containing MB fiber alone, exhibiting a greater extent of crack length. At a volume fraction of 0.9% for MB fiber and 0.2% for PVA fiber, a significant improvement in the fatigue life of the concrete was observed, resulting in a remarkable 136.23% increase compared to the control. This study has developed geopolymer concrete featuring enhanced crack resistance and superior flexural fatigue endurance under cyclic loading, promoting the application of environmentally friendly building materials in practical engineering.

Enhancing Porous Asphalt Performance by Adding Waste Mask Fiber: Experimental Analysis of Stiffness, Fatigue, and Creep at Optimum Asphalt Content

Purpose: This study aims to evaluate the impact of incorporating waste mask fibers into porous asphalt mixtures, focusing on stiffness, fatigue, and creep performance at the optimum asphalt content (OAC). Theoretical Reference: The study is based on sustainable construction and materials engineering theories, emphasizing the recycling of waste materials to enhance the performance of construction materials and mitigate environmental impacts. Method: Laboratory experiments were conducted by adding waste mask fibers at varying levels (0%, 1%, 2%, and 3% by weight of asphalt) to the porous asphalt mixtures. Test specimens were designed and evaluated for stability, flow, Marshall Quotient, Voids in Mineral Aggregate (VIM), indirect tensile strength (ITS), stiffness (ITSM), fatigue, and creep performance. Results and Conclusion: The addition of 1% waste mask fibers at the OAC is recommended as it meets the criteria for stability, flow, Marshall Quotient, and VIM. The Cantabro Test showed enhanced resistance, while the ITS Test indicated increased indirect tensile strength. The ITSM Test revealed heightened stiffness of the mixture. Although fatigue testing demonstrated that the porous asphalt mixture could bear loads until collapse at a certain stress level, the creep test confirmed the mixture's resistance to permanent deformation due to traffic loads. Implications of research: The findings suggest that incorporating waste mask fibers into asphalt mixtures can improve mechanical properties and durability, offering a sustainable solution for mask waste disposal. This approach can be adopted by policymakers and engineers to enhance road construction practices while addressing environmental concerns. Originality/value: This study provides novel insights into the recycling of waste mask fibers in asphalt mixtures, demonstrating their potential to improve performance and sustainability in road construction. The research offers a pioneering approach to addressing the environmental challenges.

Characterisation of bitumen through multiple ageing-rejuvenation cycles

ABSTRACT The multiple recycling of bitumen offers the possibility of reusing it for repeated lifecycles and achieve a higher degree of circularity of materials used in pavement construction. Aiming to identify the prospect, this study aged bitumen in a laboratory setting and then rejuvenated it using a bio-based rejuvenator for four ageing cycles. The low temperature and fatigue performance of the bitumen in each cycle was comprehensively characterised using dynamic shear rheometer (DSR) based rheological measurements. The results illustrated that although rejuvenation cannot recover all properties of the aged bitumen to the level of virgin bitumen, using rejuvenators can largely improve most properties negatively affected by ageing. The optimal dosage of rejuvenators should be determined based on the balance of the properties. The use of rejuvenation indexes, such as the one employed in this study, can assure that the low-temperature and intermediate temperature performance can be met through multiple ageing-rejuvenation cycles. In terms of chemical changes, although ageing reduces the chemical or colloidal stability of bitumen, rejuvenation can recover this property to its initial level. Overall, the results obtained in the study suggest that using appropriate rejuvenators, bitumen can potentially be recycled through multiple lifecycles.

The effect of runoff acidity on fatigue cracking of hot mix asphalt using thermodynamic concepts

This study examined the fatigue performance of hot mix asphalt (HMA) under the influence of runoffs entering the pavement with different acidity degrees. Based on the fatigue test results, changing the runoff acidity and increasing the temperature decreased the number of cycles leading to HMA fracture (fatigue life) and accelerated the damage. The results of the surface free energy (SFE) method were aligned with the fatigue test results, indicating that changing the runoff acidity increased the bitumen-water adhesion SFE, aggregate-water adhesion SFE, and bitumen-aggregate debonding SFE. These changes diminished the fatigue cracking resistance of HMA. According to the Pull-Off test results, altering the runoff acidity and increasing the temperature reduced the adhesion and cohesion strength. According to the two principal factors in fatigue cracking (fracture adhesion and cohesion), the reduced fatigue life of the samples due to variations in the runoff acidity and temperature increase was acceptable according to the SFE and Pull-Off test results. The independent samples t test revealed that changing the runoff acidity led to a significant decline in the asphalt samples' performance parameters compared to neutral conditions.

Revealing the failure mechanism of industrial Fe-25Cr-20Ni stainless steel plate: Fine-grained segregation band and brittle phase induced delamination cracking

The use of heat-resistant stainless steel thick plates in industrial production often presents challenges due to the presence of uneven microstructure and segregation, which can pose a persistent challenge for the prolonged safe operation of critical components made from such materials. This study aimed to investigate the fracture mechanism of an industrial Fe-25Cr-20Ni stainless steel plate at room temperature through uniaxial tensile experiments and fully reversed strain-controlled tension-compression fatigue experiments. Delamination cracks were observed on the fracture surfaces of both experiments. The specimens with fracture delamination were systematically studied by detailed microstructural evolution, and the failure mechanism and main reasons of fracture delamination were analyzed. The results show that the fracture delamination is related to the fine-grained segregation band (FGSB) consisted of fine grains and sigma phase located at the center of the thickness of the stainless-steel plate. The FGSB demonstrates low transgranular and intergranular fracture modes and exhibits bamboo knobs crack during plastic deformation, leading to a mixed fracture mode of ductile and brittle fracture. Furthermore, FGSB, as an anisotropic microstructure, which has a high stress concentration with nearby grains during plastic deformation. The sigma phase fracture and the weakening of the interface strength of the microstructure in FGSB provide a potential initiation site for fatigue crack initiation, thereby contributing to the possibility of aggravating fatigue damage and deteriorating fatigue performance. It is concluded that FGSB, as a metallurgical defect in stainless steel plates, is responsible for delamination failure.

Mechanisms affecting the difference in fatigue resistance between welds and base materials were investigated based on in-situ fatigue method

Coiled tubing (CT) is manufactured using plastic processing and weld molding techniques, rendering the weld zone (WZ) susceptible to fatigue fractures under the continuous action of complex alternating loads during field applications. While this risk has garnered significant attention, the underlying mechanisms of its fatigue failure remain elusive. To address this knowledge gap, this study employs an in-situ SEM fatigue test method, coupled with metallographic analysis, hardness testing, SEM observation, and EBSD characterization, to deeply analyze the fatigue microdamage mechanism in the WZ by comparing the fatigue performance of the base material (BM) of the CT with that of WZ. It is found that the microstructure of the BM consists of different scales and shapes of ferrite and a small amount of pearlite nested and intertwined with each other, which has a strong coordinated deformation ability and can effectively relieve stress concentration, delay crack initiation and form a single fatigue source. In contrast, the WZ’s ferrite organization is large, uniform, and independent, making it prone to early-stage plastic deformation with weak inter-grain coordination, resulting in the formation of numerous slip bands and multiple crack sources. During the crack propagation stage, the abundant grain boundaries in the BM effectively deflect the crack expansion direction and slow down its progression; while multiple secondary cracks in the weld expand simultaneously and connect with each other, resulting in a higher crack expansion rate than the BM. The research findings provide crucial insights and guidance for enhancing the overall fatigue performance of CT.

Fatigue design of stress relief grooves to prevent weld root fatigue in butt-welded cast steel to ultra-high-strength steel joints

In the welded joints, fatigue failures typically originate from defects or notch-like geometries under cyclic loading. This study investigates the impact of stress relief grooves (SRG) on the fatigue performance of butt-welded cast steel to ultra-high-strength steel components using experimental fatigue tests and finite element method. The experiments examined the fatigue properties of hybrid joints between G26CrMo4 cast steel (t = 20 mm) and S960 steel plate (t = 6 mm) with and without SRG. Gas metal arc welding process was used to weld the butt joints that had a permanent root backing machined on the cast steel part, causing a crack-like defect to the weld root. Additionally, the top surfaces of the welded parts were aligned, resulting in a significant axial misalignment in the butt joint. The SRG, positioned close to the weld root, was found to have a beneficial influence on the joint’s fatigue performance by a factor of 1.2 when using the nominal stress criterion. However, the fatigue capacity was still roughly 35% lower compared to the symmetrical equivalent due to the secondary bending stress, caused by axial misalignment. The finite element analyses indicated that the SRG reduces the amount of secondary stresses at the weld root leading to lower total structural stress. The study recommends using the FAT80 (m = 3) design curve in the structural stress method, for similar butt-welds having a crack-like defect, parallel to the loading direction, at the weld root. However, for welded joints with crack-like defects, it is advisable to use linear elastic fracture mechanics rather than relying solely on stress-based local approaches.

Study on fatigue-healing performance and life prediction of hot recycled asphalt mixture

The extensive application of recycled asphalt mixtures (RAM) requires a better understanding of its fatigue performance and there is need to establish an accurate prediction model for fatigue life. The fatigue-healing performance of RAM containing different recycled asphalt pavement (RAP) contents was investigated by using four-point bending test with virgin mixtures as a reference. The linear portion during the steady decline of the flexural stiffness was utilized to establish a linear method for fatigue life prediction. The effects of RAP content, aging, and immersion factors on the fatigue-healing performance of RAM were studied. A fatigue-healing life prediction model considering RAP content, initial flexural stiffness (E0), strain level, long-term aging at 85 °C and moisture immersion at 60 °C was developed through regression analysis of data obtained from various fatigue tests. The test results indicated that E0 at the 500th loading cycle exhibited higher accuracy for life prediction based on linear rule when compared with the traditional E0 at the 50th loading cycle. With an increase in RAP content, the fatigue life of RAM decreased, while the E0 showed a linear increase and the healing index gradually decreased. The decrease in fatigue life of RAM due to moisture effect was greater than that due to long-term aging effect. Aging effect for 5 d and moisture immersion for 7 d reduced the fatigue life of RAM by 17.9 % and 47.4 % respectively. The fatigue-healing life prediction model can accurately predict the fatigue life of RAM within the range of 0–45 % RAP content. Aging was found to have the greatest negative effect on the healing performance of RAM, followed by moisture effect, while the effect of RAP content was minimal. This study contributes to the prediction of remaining fatigue life for RAM after long-term service and improving its service levels.

Evaluating and correlating asphalt binder and mixture fatigue properties considering aging conditions

Asphalt fatigue cracking is a critical distress type for flexible pavement. This study utilized the state of practice binder and mixture cracking tests and parameters to investigate how asphalt binders’ and mixtures’ fatigue performance vary between the different mix designs and evaluate their changes with aging. The potential relationships between the measured binder properties and mixture performance were also explored. Five asphalt mixtures with disparate mix designs were evaluated and three different aging conditioning levels were conducted. The binder tests include the traditional time and frequency sweep and linear amplitude sweep test, while the mixture evaluations include the semi-circular bending and cyclic fatigue test. The results indicate that the different fatigue parameters from the tests can evaluate and rank the mixes differently. The correlation analysis using the Spearman correlation coefficient shows that the mixture cracking parameters that are more predominant by asphalt mixture’s flexibility/brittleness show strong correlations (Spearman coefficient larger than 0.8) with binder cracking indices. The LAS fatigue life-related parameters generally do not correlate well with mixture fatigue indices (Spearman coefficient smaller than 0.6). Furthermore, a prediction model to estimate asphalt mixture’s fatigue performance was developed based on linear regression and Artificial Neural Network (ANN) approach, which only requires the mix design info. and binder fatigue property as the inputs, significantly reducing the time and eliminating the effort in preparing and testing the asphalt mixture specimen for mixture fatigue performance measurement.

Cyclic damage quantification in composite materials using discrete damage mechanics

A method for fatigue damage quantification in composite materials, based on experimental stiffness degradation data for composite laminates subjected to cyclic load is proposed. Discrete damage mechanics theory is used to calculate crack density vs. number of cycles from elastic moduli-reduction data obtained during fatigue experiments. The calculated crack density simplifies fatigue testing by diminishing the need for counting cracks during testing. Accurate results are achieved and reported. The defect-nucleation rate, which controls the fatigue damage rate, is also obtained from processing the modulus-reduction data. It is observed that the defect-nucleation rate has a small scatter and is independent of applied load magnitude. Furthermore, the onset of delamination observed in the experiments correlates very well with the onset of deviation between the predicted and experimental curves of elastic moduli-reduction versus accumulated crack density. An additional parameter, the defect-nucleation threshold, is here proposed to further characterize the fatigue performance of the composite material under stress-controlled fatigue loading, in contrast to thermal fatigue results from the literature. Furthermore, the difference in damage nucleation rate between strain-controlled and stress-controlled was observed and discussed.

Effects of post-processing and loading orientation on high-cycle fatigue of selective laser melted Ti-6Al-4V

Recent research on selective laser melted (SLM) Ti-6Al-4V showed that fatigue fracture differs depending on the post-processing and loading orientation. To better understand their influences, tensile and fatigue tests on samples with three post-processing conditions, namely, stress relief (SR), Sub-transus and hot-isostatic-pressing (HIP), were conducted in both the vertical and horizontal loading orientations. The elongation-to-failure of horizontal specimens are consistently higher than the vertical ones for the SR and Sub-transus state, but the opposite trend is observed for the HIP state. This discrepancy is owing to the reduced defect in combination with the {112¯0}α preferred orientation. Comparison of the SR and Sub-transus states suggests that coarser α-lath contributes to a longer initiation phase of microcrack from the defect, which improves overall fatigue performance. Fatigue strength of the HIP state is significantly higher than the other two states, exhibiting little anisotropy, and the fatigue-cracking source shifts from the defect to the microstructural facet. Subsequently, a model is proposed to evaluate the high-cycle fatigue of SLM-built Ti-6Al-4V, by incorporating yield strength and elongation-to-failure as additional variables, achieving the life prediction error band within two to five times with respect to the experimental data.

Fatigue Behaviors and Dislocation Evolution of Copper and Aluminum Alloy

Face‐centered cubic (FCC) metals are widely used in the field of structural materials due to their excellent mechanical properties, and their fatigue behaviors have always been a focus of attention. Herein, 1060 aluminum alloys with different processing states and copper are selected to study the high cycle fatigue performance at room temperature and high temperature. The fracture morphology and dislocation evolution are characterized through characterization methods such as scanning electron microscope and transmission electron microscope. Based on the research, the main movement mode of dislocations (plane slip or wavy slip) are influenced by stacking fault energy (SFE), which further has a significant impact on fatigue performance. When the SFE of the FCC metal is higher, wavy slip dominates and the material is sensitive to temperature changes; on the contrary, during cyclic loadings, metal with lower SFE is dominated by plane slip, due to the reversibility of plane slip, the damage to the material with low SFE under fatigue loading is more uniform.

Pseudo-twin boundary improves flow stress and cyclic stability of TiAl single crystal

Polysynthetically twinned (PST) TiAl single crystal with lamellar structures exhibits great mechanical properties at room temperature. Therein twin boundaries (TBs) are important for achieving optimized ductile and fatigue performance of PST TiAl, but their role and the associated mechanism are elusive. Herein, we decipher the role of true TB (TTB) and pseudo TB (PTB) by a combined atomistic simulation and mesoscopic modeling, and find that PTB could remarkably improve room-temperature flow stress and cyclic stability of TiAl single crystal. It is revealed that dislocations pile up at PTB while unobstructedly traverse TTB. The emergency of back stress and the movement of dislocations along PTB contribute to the strengthening mechanism. The flow stress of TiAl single crystal with PTB is 34% higher than that with TTB. It is further found that as the twin thickness decreases, the flow stress of TiAl single crystal with TTB initially increases and then decreases (i.e., inverse Hall–Petch like behavior), whereas that with PTB always increases owing to the extra back stress and interfacial stress (i.e., Hall–Petch like behavior). Atomistic-informed mesoscopic theoretical models are then proposed to describe the flow stress as a function of twin thickness. Under cyclic loading, PTB is found to facilitate strain delocalization of TiAl single crystal during plastic deformation and thus noticeably improve the cyclic stability. These findings should shed light on achieving strong TiAl alloys with enhanced fatigue performance by the introduction and design of PTB.

Correlative spatter and vapour depression dynamics during laser powder bed fusion of an Al-Fe-Zr alloy

Spatter during laser powder bed fusion (LPBF) can induce surface defects, impacting the fatigue performance of the fabricated components. Here, we reveal and explain the links between vapour depression shape and spatter dynamics during LPBF of an Al-Fe-Zr aluminium alloy using high-speed synchrotron x-ray imaging. We quantify the number, trajectory angle, velocity, and kinetic energy of the spatter as a function of vapour depression zone/keyhole morphology under industry-relevant processing conditions. The depression zone/keyhole morphology was found to influence the spatter ejection angle in keyhole versus conduction melting modes: (i) the vapour-pressure driven plume in conduction mode with a quasi-semi-circular depression zone leads to backward spatter whereas; and (ii) the keyhole rear wall redirects the gas/vapour flow to cause vertical spatter ejection and rear rim droplet spatter. Increasing the opening of the keyhole or vapour depression zone can reduce entrainment of solid spatter. We discover a spatter-induced cavity mechanism in which small spatter particles are accelerated towards the powder bed after laser-spatter interaction, inducing powder denudation and cavities on the printed surface. By quantifying these laser-spatter interactions, we suggest a printing strategy for minimising defects and improving the surface quality of LPBF parts.

An investigation on bending fatigue in a corrosive environment of dual-phase 1000 sheet steel RSW joints and damage model via experiment and numeric analysis

Fatigue, corrosion, and fatigue damage models are best addressed to improve and understand the service performance of materials, particularly automotive steel. This study is an attempt to experimentally and finite element investigates plain bending fatigue performance and damage model of DP 1000 sheet steel resistance spot welding (RSW) joints in 3% NaCl aqueous corrosive treatment. RSW applications were carried out using different weld currents. The joint samples were then subjected to optical image analysis, tensile shear, and fatigue tests (3% NaCl-aqueous and normal atmosphere). A proper damage model of RSW junctions was developed and corrected by numeric analysis. Besides, RSW nugget formation, tensile shear, and plain bending fatigue tests were also applied. Consequence, fatigue behavior, tensile load carrying capacity, and effective fracture behavior of resistance spot welded joint specimens were evaluated. Results showed that a corrosive environment negatively affected fatigue performance. With the developed model, it was observed that the fatigue life of the samples decreased by 30–35% in the fatigue tests performed in the corrosive environment. Experimental and numerical analysis results of plain bending were compatible.

Effect of SARA Fractions on Fatigue Properties of Hard Asphalt.

The fatigue performance of hard asphalt is an important factor that affects the service life of asphalt pavement. In order to comprehensively explore the influence of chemical components on the fatigue performance of hard asphalt, and to eliminate the chemical instability between the microstructure of asphalt from different oil sources, seven kinds of hard asphalt were designed and prepared with saturates, aromatics, resins, and asphaltenes (SARA) extracted from the same hard asphalt. Rheological, time sweep and linear amplitude sweep (LAS) tests were carried out to evaluate the fatigue properties. The results show that the complex modulus of asphalt binds increased rapidly with an increase of asphaltene and resins and that the colloidal structure was strengthened, which would increase the fatigue factor. In the time sweep test, the strength of the colloidal structure significantly affected the fatigue life, and the fatigue life was different under different test stresses. In the viscoelastic continuum damage (VECD) model, the cumulative damage was related to the modulus, while with the increase of asphaltene and resins, the fatigue life showed a trend of first increasing and then decreasing. The linear regression analysis showed that the fatigue life of hard asphalt had a good correlation with strain sensitivity. This study investigated the applicability of different fatigue evaluation methods and revealed the influence of four components on the fatigue properties of hard asphalt. The results provide significant insights in the improvement of the fatigue performance of both hard asphalt and corresponding mixtures.

Design, fabrication, and clinical characterization of additively manufactured tantalum hip joint prosthesis

Abstract The joint prosthesis plays a vital role in the outcome of total hip arthroplasty. The key factors that determine the performance of joint prostheses are the materials used and the structural design of the prosthesis. This study aimed to fabricate a porous tantalum (Ta) hip prosthesis using selective laser melting (SLM) technology. The feasibility of SLM Ta use in hip prosthesis was verified by studying its chemical composition, metallographic structure, and mechanical properties. In vitro experiments proved that SLM Ta exhibited better biological activities in promoting osteogenesis and inhibiting inflammation than SLM Ti6Al4V. Then, the topological optimization design of the femoral stem of the SLM Ta hip prosthesis was carried out by finite element simulation, and the fatigue performance of the optimized prosthesis was tested to verify the biomechanical safety of the prosthesis. A porous Ta acetabulum cup was also designed and fabricated using SLM. Its mechanical properties were then studied. Finally, clinical trials were conducted to verify the clinical efficacy of the SLM Ta hip prosthesis. The porous structure could reduce the weight of the prosthesis and stress shielding and avoid bone resorption around the prosthesis. In addition, anti-infection drugs can also be loaded into the pores for infection treatment. The acetabular cup can be custom-designed based on the severity of bone loss on the acetabular side, and the integrated acetabular cup can repair the acetabular bone defect while achieving the function of the acetabular cup.

Multi-Objective Process Parameter Optimization of Ultrasonic Rolling Combining Machine Learning and Non-Dominated Sorting Genetic Algorithm-II.

Ultrasonic rolling is an effective technique for enhancing surface integrity, and surface integrity is closely related to fatigue performance. The process parameters of ultrasonic rolling critically affect the improvement of surface integrity. This study proposes an optimization method for process parameters by combining machine learning (ML) with the NSGA-II. Five ML models were trained to establish relationships between process parameters and surface residual stress, hardness, and surface roughness by incorporating feature augmentation and physical information. The best-performing model was selected and integrated with NSGA-II for multi-objective optimization. Ultrasonic rolling tests based on a uniform design were performed, and a dataset was established. The objective was to maximize surface residual stress and hardness while minimizing surface roughness. For test specimens with an initial surface roughness of 0.54 µm, the optimized process parameters were a static pressure of 900 N, a spindle speed of 75 rpm, a feed rate of 0.19 mm/r, and rolling once. Using optimized parameters, the surface residual stress reached -920.60 MPa, surface hardness achieved 958.23 HV, surface roughness reduced to 0.32 µm, and contact fatigue life extended to 3.02 × 107 cycles, representing a 52.5% improvement compared to untreated specimens and an even more significant improvement over without parameter optimization.

The effects of VAR interventions on self-rated mental fatigue and self-rated performance of football referees

ABSTRACT Football referees are required to make numerous decisions per match under physiological and emotional strain. Within this context, VAR (video assistant referee) interventions represent a key match event in which referees’ critical decisions are challenged and thus their perceived ability to control the match might also be obscured. In this study, we investigated the effects of a VAR intervention on referees’ self-rated mental fatigue (MF) and performance. Nine elite referees completed over 2–6 real matches each (total of 44 matches) a single item of MF before the match, at half-time, and immediately after the match. Situational and performance indices were also collected. The referees’ level of MF significantly increased from pre-match to half-time to post-match, yet the referees were not completely mentally fatigued at the end of the matches. Post-match MF was higher (a medium effect) for matches with a VAR intervention (n = 9) compared with matches without an intervention (n = 35). Post-match MF correlated negatively with self-rated performance, r(44) = .35, p = .019. These findings are discussed in relation to current theory and research in the area of self-control and MF in sports. We also provide recommendations for referee training and match preparation.

Multiaxial Fatigue Damage Analysis of Steel–Concrete Composite Beam Based on the Smith–Watson–Topper Parameter

The fatigue performance of steel–concrete composite beams is crucial for ensuring structural safety. To account for the member’s multiaxial stress state, this study employed the critical surface method, using fatigue damage parameters as an evaluation index for assessing fatigue performance. Static and fatigue performance tests on steel–concrete beams were conducted to identify failure characteristics, which informed the development of a finite element model that incorporates concrete damage. Using the SWT model, the most unfavorable loading parameters were determined by analyzing critical paths on the test beams, providing a basis for predicting how initial defects impact fatigue performance. The impact of initial defects on the fatigue performance of the composite beam is assessed using this criterion. The results indicate that the discrepancy between the actual and predicted load capacities of the test beam is within 5%, and cyclic loading significantly affects the test beam’s mechanical properties, resulting in a 27% reduction in load capacity and a 48% increase in deflection after 2 million cycles. Finite element modeling reveals that components experience multiaxial stress, with test beam mechanical property changes aligning with predicted fatigue damage parameters, confirming the reliability of using these parameters as a criterion. As the strength of the composite beams diminished due to pore defects, the fatigue damage parameter escalated, increasing the likelihood of crack formation. However, once the concrete’s strength fell to a level where the pegs were insufficiently constrained, the structural damage pattern shifted, and the fatigue damage parameter subsequently decreased.