External Load Research Articles

Analysis of Vibration Characteristics of Spatial Non-Uniform Tensioned Thin-Film Structures Based on the Absolute Nodal Coordinate Formulation.

Due to their lightweight characteristics, spatial thin-film structures can generate vibrations far exceeding their film thickness when subjected to external loads, which has become a key factor limiting their performance. This study examines the vibration characteristics of tensioned membrane structures with non-uniform elements subjected to impacts in air, leveraging the Absolute Nodal Coordinate Formulation (ANCF). This model takes into account the wrinkling deformation of thin films under pre-tension and incorporates it into the dynamic equation derived using the absolute node coordinate method. A detailed discussion was conducted on the influence of non-uniform elements, situated at different locations and side lengths, on the vibration characteristics of the thin film. The analytical results obtained from the vibration model were compared with the experimental results, validating the effectiveness of the vibration model. This provides a theoretical foundation for the subsequent vibration control of thin films.

Thermoelectric generator efficiency: An experimental and computational approach to analysing thermoelectric generator performance

TEGs are devices that convert heat directly into electricity through the Seebeck effect, offering a promising solution for waste heat recovery in various industries. In this research, COMSOL Multiphysics 6.0 was used to conduct a comprehensive 3-dimensional computational study of TEGs. Integrating thermal and electrical models in COMSOL facilitates a detailed understanding of the thermoelectric phenomenon. Applying six distinct temperature gradients, temperature and electrical distribution, power output, and efficiency of the TEG was thoroughly analysed. Experimental validation confirms strong agreement between simulation and experimental data, emphasizing accuracy. The average efficiency for the TEG at 1 Ω load is 3.12 %, increasing to 3.62 % for a 2 Ω load. The relative error between the computational model and the experimental model was 5 % for open circuit, 12.56 % for closed circuit at 1 Ω, and 12.14 % for closed circuit at 2 Ω, affirming the accuracy of the computational approach. Therefore, the computational model is validated by experimental results.Moreover, the findings highlight the relationship between external load resistance and power output, revealing that the maximum output power was achieved when the external load resistance matched the internal load resistance at 2 Ω. This work also significantly contributes to advancing the computational modelling of TEGs, validated through rigorous experimental analysis.

Electrical and piezoresistive properties of ultra-high toughness cementitious composite incorporating multi-walled carbon nanotubes: Testing, analyzing, and phenomenological modeling

This study explores the electrical and piezoresistive properties of ultra-high toughness cementitious composites (UHTCC) enhanced with multi-walled carbon nanotubes (MWCNTs) ranging from 0 to 1 wt% of cementitious binders. The observed polarization behavior is found to be analogous to the charging process of a capacitor. The polarization process and resistivity drift over time in the piezoresistive response are explained using an existing equivalent electrical circuit model incorporating a capacitor. The average results of electrical conductivity initially decrease and subsequently increase with higher MWCNTs concentrations, a phenomenon attributed to increased porosity and reduced matrix conductivity. The percolation threshold is identified at a volume fraction of 0.00387. Notably, even in the absence of MWCNTs, UHTCC materials exhibit piezoresistive properties due to the presence of metal impurities and ionic compounds. The insufficient polarization process results in an increasing trend in fractional change in resistance (FCR). The highest FCR sensitivity to external load occurs within the percolation threshold. Additionally, three equations are proposed to calculate electrical conductivity, incorporating the effects of interfaces, porosity, and matrix conductivity reduction, which align well with the experimental findings. These insights contribute to a deeper understanding of the electrical properties of UHTCC-MWCNTs composites, enabling more precise conductivity measurements and improved sensor sensitivity.

A strain-based J-integral formulation for an internal circumferential surface crack of pipeline under inner pressure and large axial deformation

The presence of cracks on pipelines poses a potential threat to their operational status, and it is critical to assess the permissibility of pipelines containing cracks. The dimensional analysis combined with the finite element method is applied to investigate the fracture behavior of circumferential crack on the internal surface of pipe under internal pressure and large axial deformation. Dimensionless parameters are determined to represent the effects of crack size, pipe geometry, pipe material, and external load on the crack front driving force, and a strain-based J-integral formulation is obtained by a stepwise coefficient fitting approach rather than a polynomial fitting method. This J-integral formula can be used to quickly assess the crack front driving force of a pipe in service condition and subjected to axial displacement. The diameter-to-thickness ratio of the pipe and the dimensionless pressure of the pipe are found to act together in a combined form on the crack front driving force. Increases in dimensionless crack depth, dimensionless crack length, the ratio of circumferential stress to yield strength of the pipe, and strain hardening exponent cause an increase in the crack front driving force. The effect of dimensionless crack depth on crack front driving force is more significant than other dimensionless parameters. Changes in the other dimensionless parameters do not significantly change the crack front driving force when the dimensionless crack depth is small. Other dimensionless parameters have a progressively greater influence on the crack front driving force as the crack dimensionless crack depth increases. Large deformations in the ligament zone and increasing axial stress are the main reasons for the high crack front driving force. The J-integral formula has a similar form to that of the J-integral in the Electric Power Research Institute (EPRI) method when the effect of internal pressure is not considered. It can be reduced to predict the crack front driving force of a surface cracked plate subjected to uniaxial tensile loading. For the interaction between an internal surface crack and an embedded crack, re-characterizing the crack size using BS 7910 will overestimate the equivalent crack depth, and a more accurate equivalent crack size can be obtained using the J-integral formula proposed.

Determination of critical local straining conditions for solidification cracking at laser beam welding by experimental and numerical methods

AbstractThe phenomenon of solidification cracking has been the subject of numerous research projects over the years. Great efforts have been made to understand the fundamentals of hot cracking. It is generally agreed that solidification cracks form in the solidification range between the liquidus and solidus temperatures under the combination of thermal, metallurgical and mechanical factors. There is still a need to determine the time‐resolved strain distribution in the crack‐sensitive region in order to analyse the local critical conditions for solidification cracking phenomena. This was a strong motivation for the development of a measurement system used in this study to estimate the local strains and strain rates in the zone where the solidification crack is expected to occur. The laser beam welding experiments were conducted using the Controlled‐Tensile‐Weldability test (CTW test) to apply an external strain condition during welding to generate solidification cracks. The CTW test is a test method for investigating the susceptibility of laser‐welded joints to solidification cracking, in which the sample can be subjected to a defined strain at a defined strain rate during welding.In combination with experimental investigations, numerical simulations provide spatially detailed and time‐dependent information about the strain development during the welding process, especially regarding the critical conditions for solidification cracking. Therefore, this tool was also used in the present study to evaluate the accuracy of measurement methods and to estimate experimentally derived values and their concrete influence on the formation of solidification cracks. By integrating experimental methods and numerical simulations, this study investigates the spatially resolved and temporally changing development of strain during welding, with a particular focus on the critical conditions that lead to the formation of solidification cracks. The use of numerical simulations serves a dual purpose by validating the accuracy of measurement methods and examining experimentally determined values for their actual influence on the formation of solidification cracks. A three‐dimensional finite element (FE) model implemented with ANSYS is used to simulate strains and stresses during welding. The credibility of the model was first established by validation using experimental temperature measurements. Subsequently, structural simulations were carried out under external load. The results of the simulations showed commendable agreement with the strain measurements performed using the developed technique.

Characterization of Nano-kaolin and its enhancement of the mechanical and corrosion resistance of epoxy coatings

This study compares the effects of varying concentrations of nano-kaolin and titanium dioxide on the mechanical and corrosion resistance of epoxy coatings. Characterization techniques such as TEM, XRD, Raman, FTIR, XPS, and AFM revealed surface features of nano-kaolin: the particle size reached the nanoscale, the XRD diffraction peak at 2θ = 25.3° disappeared, Raman peaks broadened with decreased intensity, and a blue shift occurred in the FTIR spectra for various functional groups. Compared to pure epoxy coatings, the composite epoxy coating with 10 wt% nano-kaolin showed an 83.87 % increase in adhesion, an 81.82 % improvement in impact resistance, and a 61.42 % reduction in friction coefficient; while a 20 wt% titanium dioxide composite coating showed a 74.19 % increase in adhesion, a 75.76 % improvement in impact resistance, and a 46.9 % reduction in friction coefficient. Electrochemical tests indicated that a composite coating with 10 wt% nano-kaolin, after soaking in 3.5 wt% NaCl solution for 960 hours, achieved a corrosion efficiency of 98.87 % and an impedance modulus of 108.8Ω.cm2, which was three orders of magnitude higher than that of pure epoxy resin, increasing corrosion resistance by 57.14 %; whereas a 20 wt% titanium dioxide composite coating reached a corrosion efficiency of 89.29 % and an impedance modulus of 106.6Ω.cm2 after the same conditions, increasing corrosion resistance by 17.86 % compared to the pure epoxy resin. The composite coating with 10 wt% nano-kaolin exhibited superior mechanical and corrosion resistance, outperforming the 20 wt% titanium dioxide coating. Mechanical and corrosion mechanisms suggest that the uniformly dispersed nano-kaolin inhibits interactions between epoxy resin molecules and carries the external load, thereby enhancing intermolecular cohesion. Improved adhesion and impact resistance indirectly extend the coating's lifespan by prolonging the path of corrosion media through the coating to the substrate. The novel coating modification method proposed in this study effectively replaces titanium dioxide and enhances the coating's mechanical and corrosion resistance, offering a new solution for corrosion prevention in metal materials.

The Impact of a Congested Competition Schedule on Load, Recovery, and Well-Being in Under-16 Female Soccer Players: A Comparison between Starters and Non-Starters during a Development Tournament

Monitoring training load, recovery, and wellness in maturation ages is even more relevant than in adulthood, especially during congested schedules. The objective of this study was to quantify and describe the differences in external and internal load, recovery, and perceived wellness in elite under-16 female players during a period of three competitions in seven days based on their participation during matches. An observational design was used to quantify the external load (total distance, high-speed distance, and PlayerLoad) and internal load (differential sRPE), as well as the recovery and wellness of 18 international under-16 players during a development tournament. The external load pattern of the starting players was undulating, with matches showing the highest internal load values compared to training sessions and non-starters. Non-starter players (whether training or matches) showed similar external load and differential sRPE values throughout the tournament (p > 0.05). Starting players experienced higher internal load than non-starters during matches (p < 0.037), without differences between training sessions (p > 0.05). No changes were seen in wellness or recovery (all p-values > 0.05), except for non-starters in Session 3 compared to Session 7 (p = 0.024). Starting players had more weekly total minutes (p = 0.018), differential sRPE (breath: p = 0.002; leg: p = 0.002; cognitive: p = 0.003), total distance (p = 0.003), and PlayerLoad (p = 0.008) than non-starters. Our results indicate differing load patterns between starters and non-starters, which do not affect wellness and recovery differently. Starters accumulate more weekly total load. Coaches can use these findings to guide decisions and load compensations in high competition contexts for young female soccer players.

Performance evaluation of microbial fuel cells for bioelectricity generation: influence of potential scan-rate and real-time external load

AbstractThe electrochemical performance of microbial fuel cells is conventionally assessed through linear sweep voltammetry at predefined potential scan rates. Nevertheless, this approach frequently falls short in representing the long-term behavior of microbial fuel cells under actual external loads, highlighting the need for a standardized evaluation method incorporating both linear sweep voltammetry and external loads. To address this gap, this study evaluates the performance of single-chamber microbial fuel cells under different loads and scan rates. The MFCs were tested with external loads of 1200, 470, and 270 Ω, derived from maximum power points of polarization sweeps at scan rates of 0.1, 0.5, and 1 mV/s at two operational phases. Power estimates at these scan rates were 61.96, 87.88, and 166.68 mW/m2 at current densities of 116.5, 229.6, and 403 mA/m2, respectively. In the initial two hours, average power densities with 1200, 470, and 270 Ω were 73 ± 16.7, 36.3 ± 42, and 88.5 ± 120.1 mW/m2, respectively. Over the long term, the fuel cells under constant loading with resistance estimated at 0.1 mV/s showed average power 73.7% and 89.1% higher than those with resistances estimated at 0.5 mV/s and 1 mV/s, respectively, indicating that higher scan rates lead to overestimation of power. Although initially underestimated, the 0.1 mV/s scan rate more accurately reflected the true long-term performance of the fuel cells. This study emphasizes the importance of using appropriate scan rates for linear sweep voltammetry to obtain realistic long-term performance estimates of microbial fuel cells under real-time loads.

Nonlinear optimal frequency control for dynamic vibration absorber and its application

A principal limitation of passive dynamic vibration absorber (DVA) lies in its intrinsic design constraint, as it is tuned to a specific resonant frequency, rendering it less effective at mitigating vibrations over a variable frequency range. To ensure that the DVA retains its vibration reduction capability under loads with time-varying frequencies, this paper proposes a method for designing the optimal suspension frequency based on the external load frequency. The approach involves altering the stiffness of the DVA through semi-active or active control to achieve the optimal suspension frequency and the best vibration reduction performance. In this study, the ratio R between the optimal suspension frequency and the load frequency is defined, and the nonlinear characteristic of R, based on the lowest vibration transmission rate, is studied using a two degree-of-freedom DVA model. Furthermore, an optimal suspension frequency variation control strategy based on load frequency identification is presented. Combined with the typical load with time-varying frequency encountered in metro vehicles, a multi-body dynamics theoretical model and a rigid–flexible coupling dynamics model are established to verify the effectiveness of the nonlinear optimal frequency control. Finally, the full-size railway vehicle roller rig is used to verify the correctness of the principle of optimal frequency curve. The research results show that when the mass ratio is 0.1, compared with rigid suspension, the nonlinear optimal frequency control can reduce the root mean square (RMS) value of the carbody’s entire time period acceleration during variable speed operation by 62.2%, and the maximum RMS value is reduced by 83.6%. In nonlinear control, unlike passive DVA, the vibration is never higher than that of rigid suspension within a specific velocity range. Compared with linear control strategy, nonlinearity can further reduce the elastic vibration. The test results from roller rig indicate that the semi-active DVA can effectively reduce the elastic vibrations of the carbody, while also validating the correctness of the nonlinear optimal suspension frequency principle. Therefore, the nonlinear frequency control in this study can provide reference for structural vibration control under loads with time-varying frequencies.

Multiscale shear failure mechanisms within a prestrained composite

AbstractThe elastic fiber prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite, where continuous fibers were prestretched under either constant stress or constant strain throughout the curing process. The tension was only removed after the resin was fully cured. It has been demonstrated that EFP is able to enhance the shear properties of the composite, while the underlying mechanics is still unknown. Here, we investigated the multiscale shear failure mechanisms induced by the EFP within a carbon composite. A bespoke biaxial fiber prestressing rig was developed to apply biaxial tension to a plain‐weave carbon prepreg, where the constant strain‐based EFP method was employed to produce prestrained composites with different prestrain levels. Effects of EFP on macro‐scale shear failure were subsequently characterized through mechanical tests and micro‐morphological analysis. Both the micro‐ and meso‐scale representative volume element (RVE) finite element models were established and experimentally verified. These were then employed to reveal the underlying stress evolution mechanics induced by EFP. It is found that EFP would improve the shear performance of a composite by enhancing the fiber/matrix interfacial bonding strength. This attributes to the elastic strain recoveries of the prestrained fibers locked within a polymeric composite, which generate compressive stresses to counterbalance the external loading. The multiscale shear failure mechanisms were then proposed. These findings are expected to facilitate structural design and application of the EFP for aerospace composites.Highlights Biaxial tension is applied to produce prestrained woven composite. Prestrain effects on microstructural stress evolution mechanics are revealed. Multiscale shear failure mechanisms are proposed for prestrained composites.

Comparison between junior and recreational based on internal and external load response in soccer

The characteristics of soccer games tend to be at medium and high intensity. Measurement of heart rate response and activity profile can be used to assess the physical condition performance of players in planning the right program. The purpose of this study was to analyze the differences between heart rate response and activity profile in junior and recreational soccer players. The sampling technique used was purposive sampling. 24 male soccer players (12 junior Aged 11.58 ± 0.28 Years, 142.25 ± 8.74 cm, 34.5 ± 6.42 kg) and (12 recreational Aged 32.7 ± 1.38 Years, 170.67 ± 3.92 cm, 73.42 ± 5.33 kg) underwent simulation game sessions of 15 minutes each recorded using Polar Verity Sense and Catapult One to capture internal and external load data. Data were analyzed using the Mann-Whitney U Test to determine the difference between the heart rate of junior and recreational players. The results showed that there was a significant difference between HRavg in junior players (166.1 ± 17.2) and recreation (155.3 ± 10.5) as well as HRmax in junior players (193.1 ± 12.3) and recreation (176.0 ± 10.0) (p < 0.05). In addition, in the variable top speed (6.20 ± 0.68) and also maximal acceleration (4.52 ± 0.39) there is a significant difference (p < 0.05). This study concludes that there is a significant difference in heart rate response, but in the activity profile only the top speed and maximal acceleration variables between soccer players. Keywords: heart rate response, activity profile, junior and recreational soccer players

Deformation mitigation and twisting moment control in space frames

Over the last five decades, space frames have centered on the modernization of touristic zones in view of architectural attractions. Although attempts to control joint movement and minimize axial force and bending moment in such structures were made sufficiently, twisting moments in space frames have been underestimated so far. In space frames, external load or restoring the misshapen shape may cause twisting in members. We herein developed a robust computational algorithm to reduce the induced torsional moment through shape restoration within a desired limit by changing the length of active bars that are placed in space frames. Applying optimization algorithms like interior-point and Sequential quadratic programming (SQP), a direct correlation was pursued between bar length alteration and twisting in structural members. A numerical model of a single-layer space frame resembling an egg captures the twisting moment in all members, achieving a specified limit. The overall length change of the active members using an iterative process based on a heuristic that considers a threshold on the minimum length change of the active members.

The dynamic performance of semi-infinite piezoelectric strip containing irregular boundaries based on the boundary element method

In this article, the problem of a semi-infinite piezoelectric strip with irregular boundaries is studied by boundary element method, and SH guided wave and line source loads are considered as external loads acting on piezoelectric strip. The superiority of the boundary element method is induced by two different arithmetic examples. Firstly, when the irregular boundary is not subjected to line source loads, the dynamic characteristics are analyzed in the first example, employing the image method and Graf addition theorem. Then, the Green’s identities are introduced and the Green’s function in infinite three-dimensional space is solved. When irregular boundaries are subjected to line source loads, the dynamic characteristics are investigated using the boundary element method in the second example. Finally, results clarified the influence on the dynamic stress concentration factor and electric field intensity concentration factor under proper conditions. Besides, the analytical solutions are compared with the finite element solutions to verify the accuracy of the conclusions in this article.

Crack propagation in TPMS scaffolds under monotonic axial load: Effect of morphology

In this paper, the mechanical behaviour and failure of porous additively manufactured (AM) polylactide (PLA) scaffolds based on the triply periodic minimal surfaces (TPMS) is investigated using numerical calculations of their unit cells and representative volumes. The strain-amplification factor is chosen as the main parameter, and the most critical locations for failure of different types of scaffold structures are evaluated. The results obtained are presented in comparison with a multiple-crack-growth algorithm using the extended finite element method (XFEM), underpinned by the experimentally obtained fracture properties of PLA. The effect of morphology of TPMS structures on the pre-critical, critical and post-critical behaviours of scaffolds under monotonic loading regimes is assessed. The results provide an understanding of the fracture behaviour and main risk points for crack initiation in structures of AM-PLA scaffolds based on typical commonly used types of TPMS, as well as the influence of structure type and external load on this behaviour.

Mechanical evaluation of multi-continuous interpenetrating phase composites based on Schwarz Primitive cellular structure

Interpenetrating phase composites (IPCs) have been extensively promoted due to their robust mechanical properties. To further obtain the enhanced properties and elucidate the underlying mechanical mechanism, we designed and manufactured the tri-continuous IPCs by filling hyperelastic PDMS into a 3D-printed Schwarz Primitive (P) cellular skeleton based on the viscoplastic polymer. Subsequently, the compressive properties, cyclic properties, and relaxation properties of the IPCs were experimentally investigated. Results demonstrated that interpenetrating can improve the compressive properties, reduce the relaxation behavior, and weaken the cyclic softening effect. By incorporating a user material subroutine in simulations, we analyzed the deformation behaviors of P cellular material and IPCs. Through a combination of experimental observations and simulated outcomes, we refined our understanding of the deformation mechanism of IPCs. Our analysis revealed that filled PDMS played a positive role in enhancing the mechanical performance of TC-IPCs through three key mechanisms: Firstly, it shears part of the external load of TC-IPCs. Secondly, it astricts the bending deformation in the skeleton, thereby preventing the stress drop induced by buckling. Thirdly, the interaction between PDMS and P cellular skeleton puts them in compressive stress in tri-direction, enhancing the overall mechanical properties. These findings contribute to advancing the development and application of IPCs.

Improved Sliding Mode Model Reference Adaptive System Observer

In order to improve the accuracy and stability of sensorless control system of permanent magnet synchronous motor, considering the influence of external load torque on system performance, the symbol function of sliding mode control system of vehicle-mounted permanent magnet synchronous motor is prone to chattering and the robustness of traditional PI control is insufficient. In this paper, a method of combining Non-singular Fast Terminal Sliding Mode (NFTSM) and Model Reference Adaptive System (MRAS) is proposed. A Non-singular Fast Terminal Sliding Mode Controller (NFTSMC) is designed. A control strategy combining NFTSMC and Model Reference Adaptive System Observer (MRASO) (NFTSMC-MRASO) converts the observed torque value into torque current feedforward compensation to the current loop input. The large sliding mode gain is avoided, and the chattering problem of the system is overcome when the external disturbance is suddenly added. At the same time, the robustness of the system is improved under the premise of suppressing the chattering.

Quantifying the training demands of a highly trained male youth basketball players by year, term and position

ABSTRACT This study describes the training demands of highly trained male youth basketball players, based on training year, term and playing position. Data was collected from 41 male youth basketballers over two seasons from all on-court coach-led training sessions utilising an LPS. Linear mixed-models and pairwise comparisons were used to analyse by training year (Y1, Y2 and Y3), term (T1, T2, T3 and T4) and playing position (Backcourt, Frontcourt). Results showed no differences in external load metrics between training years. Significant differences existed between training terms, with total distance greater in both T3 and T4 than T1 and 2 (p < 0.03). Total PlayerLoad was significantly greater in T4 than T1 (p < 0.001) and T3 (p = 0.004). Distance/min was greater in T2, T3 and T4 than T1 (p < 0.01). PlayerLoad/min was higher in T4 than T1 and T2 (p < 0.01). Backcourt players showed significantly greater distance/min (p = 0.011), PlayerLoad/min (p = 0.011) and deceleration counts (p < 0.001). Overall, limited year-on-year change existed in external training load metrics (p > 0.05), though volume (p < 0.001) and intensity (p < 0.001) differed between terms. Backcourt players completed higher intensities (p = 0.011) than Frontcourt players. This study provides a description of external loads of training in highly trained youth basketball players assisting coaches and performance practitioners to better understand physical demands within youth basketball development pathways.

Investigation of the Permeability Function of the Contact of the Wedged Edge of a Metal Seal with a Flange under External Loads

Investigation of the Permeability Function of the Contact of the Wedged Edge of a Metal Seal with a Flange under External Loads

Pneumatic Piston Control Optimization

Abstract Piston control can be applied to regulate position, speed, acceleration, and force. The primary distinction between pneumatic and hydraulic cylinders lies in the working fluid: hydraulic systems utilize practically incompressible fluid, whereas pneumatic systems use compressible gas. Consequently, hydraulic cylinders offer more precise control over position and speed. In contrast, pneumatic cylinders are more influenced by external loads. However, pneumatic systems are simpler, more cost-effective than hydraulic systems, and more commonly used in laboratories, workshops, and production lines. They are typically employed for end-to-end motions [1] without requiring precise position control within the stroke. If a method to control pneumatic cylinders for intermediate positions within the stroke were developed, their application could be significantly expanded. In the paper titled “Pneumatic Piston Control Modelling and Optimization,” a method for controlling pneumatic pistons for industrial applications is presented [2]. Since then, the initial modelling has been further developed through practical experiments and fine-tuning. This paper summarizes the modelling efforts and introduces the experimental results.

Nonprobabilistic time-dependent reliability analysis for uncertain structures under interval process loads

In this paper, a novel nonprobabilistic analysis framework is proposed to evaluate the time-dependent reliability of uncertain structures under time-varying loads. Firstly, a novel uncertainty propagation method is developed by combining interval process integration and surrogate-based interval analysis and the correlation coefficient between responses of adjacent time steps is further analyzed. Subsequently, the nonprobabilistic time-dependent reliability is analyzed base on the first-passage theory and the established interval model. Unlike existing nonprobabilistic methods that consider time-invariant external loads, the proposed method applies an interval process to describe time-varying external loads, thereby offering a broader range of applicability. Compared to existing nonprobabilistic methods that consider time-varying loads, the proposed method establishes a more refined nonprobabilistic time-dependent reliability model based on the first passage theory, achieving higher accuracy. The effectiveness and superiority of the proposed method are validated through a numerical example and an engineering application.