Tension Fatigue Tests Research Articles

Peridynamic analysis of rolling contact fatigue crack propagation in rail welding joints with pore defects

Pore defects are prevalent in rail welding joints and significantly contribute to the propagation of fatigue cracks. This study develops a peridynamic (PD) model that incorporates the characteristics of pore defects to analyze their impact on rolling contact fatigue behavior. Initially, compact tension (CT) fatigue tests were performed to derive and validate the bond fatigue failure model specific to rail weld materials. Subsequently, pore defects were modeled as holes in the CT specimens, with experimental results being compared to PD simulation outcomes for validation. Finally, a wheel-rail contact PD model was constructed to investigate the mechanisms of fatigue crack propagation in rail welding joints affected by pore defects.

On the random vibration-based progressive fatigue damage detection and classification for thermoplastic coupons under population and operational uncertainty

The problem of vibration-based progressive fatigue damage detection and Fatigue State (FS) determination for thermoplastic coupons is experimentally addressed under significant population and experimental uncertainty. The study involves 13 coupons subjected to tension–tension fatigue testing with interruptions at 10,000-cycle intervals. Utilizing non-parametric random vibration analysis and a robust, uncertainty-tolerant methodology, the research employs Multiple Model Representations of uncertain dynamics through parametric ARMA(AutoRegressive-Moving Average)-type random vibration response modeling. Results, validated by ultrasonic C-Scan testing, reveal (a) the significance of uncertainties, (b) a resonant structural frequency indicating fatigue accumulation, (c) remarkable detection performance, achieving 100 % accuracy even at 10,000 cycles, and (d) FS determination with over 80 % accuracy across all coupons. This study offers promising avenues for automated fatigue damage detection and FS determination in thermoplastic structures, eliminating the need to interrupt their operational cycles.

Stable and wide temperature range superelasticity in an Mo-doped nanocrystalline Ni–Ti–Mo shape memory alloy

The phase transformation and superelastic behavior of nanocrystalline Ni48Ti50Mo2 alloy wires were investigated. Nanocrystalline (NC) alloys were obtained via severe plastic deformation of cold-drawing followed by annealing at low temperatures. The results indicate that the NC Ni48Ti50Mo2 undergoes a single-step B2→R phase transformation and a two-step B2→R→B19′ phase transformation in coarse crystals (CG). The NC alloy wire exhibits 8 % recoverable strain under a tensile stress of 1.1 Ga and superelasticity exists in a wide temperature range from −60 °C to 100 °C. After 50 cycles of tension fatigue testing, the superelastic upper plateau stress reduction rate is 7 % with almost no residual strain accumulation, which has excellent superelastic stability compared with fine crystals and coarse crystals. Transmission electron microscope (TEM) reveals an average grain size of 20 nm. The stable superelasticity is attributed to the nanocrystalline reinforced matrix, which hinders dislocation generation and slip.

Fatigue Crack and Residual Life Prediction Based on an Adaptive Dynamic Bayesian Network

Monitoring the health status of aerospace structures during their service lives is a critical endeavor, aimed at precisely evaluating their operational condition through observation data and physical modeling. This study proposes a probabilistic assessment approach utilizing Dynamic Bayesian Networks (DBNs), enhanced by an improved adaptive particle filtering technique. This approach combines physical modeling with various predictive sources, encompassing cognitive uncertainties inherent in stochastic predictions and crack propagation forecasts. By employing crack observation data, it facilitates predictions of crack growth and the residual life of metal structure. To demonstrate the efficacy of this method, the research leverages data from three-point bending and single-edge tension fatigue tests. It gathers data on crack length during the fatigue crack progression, integrating these findings with digital twin theory to forecast the residual fatigue life of the specimens. The outcomes show that the adaptive DBN model can precisely predict fatigue crack propagation in test specimens, offering a potential tool for the online health assessment and life evaluation for aerospace structures.

Notch effect in tension-tension fatigue of short glass fibre reinforced polyphenylene sulfide composites

An experimental investigation of the fatigue behaviour of plain and notched specimens made of 40 % wt. short glass fibre-reinforced PolyPhenylene sulfide is presented. To this end, plain and V-notched specimens (with notch root radius ranging from 0.2 mm to 10 mm) were produced by injection moulding, and the final geometries were obtained by means of two different technological processes (i.e., directly after the injection moulding process and by machining them from injected plates). To investigate the effect of notch root radius and fibre orientation, tension–tension fatigue tests were carried out in load control mode, and the experimental results were reanalysed in terms of net stress amplitude defining the traditional stress-life curves. During the fatigue tests, the damage evolution was monitored using a travelling microscope to define the number of cycles spent for fatigue crack nucleation. Furthermore, the fracture surfaces were observed at the microscopic level to investigate the damage mechanisms and the actual fibre orientation was evaluated by computed tomography analysis. Then, by employing coupled finite element analysis of the injection moulding process and the structural behaviour, four different approaches available in the open literature were used to correlate the geometrical and/or manufacturing process effects in the fatigue strength of the considered material.

Coupling effect of non‐relaxing and high temperature on fatigue properties of carbon‐black filled isoprene rubber

AbstractThis paper presents an extensive experimental investigation on fatigue properties of carbon‐black filled isoprene rubber under complex loadings. A basic life prediction model taking strain energy density as fatigue parameter is first proposed based on fatigue crack growth tests and uniaxial tension fatigue tests under relaxing loads at room temperature. A database of fatigue life including relaxing and non‐relaxing is established through a great number of fatigue tests under five temperatures. Based on the database, two empirical parameters, that is, temperature factor (NRT/NHT) and life reinforcement factor (Re), are introduced to quantitatively characterize the coupling effects of high temperature and non‐relaxing loads on fatigue life. The fatigue mechanisms under different conditions are compared via wide‐angle x‐ray diffraction tests and postmortem analysis. It reveals that the weakening of life reinforcement at high temperatures is closely related to the strain induced crystallization behavior of rubber.

Life prediction and failure analysis in laser powder bed fused TiC/Ti6Al4V titanium matrix composite under high cycle and very high cycle fatigue conditions

This study investigates the failure behavior of a TiC-reinforced titanium matrix composite (TMC) manufactured by laser powder bed fusion (L-PBF) through fully reversed and pulsating tension fatigue tests in both high-cycle and very-high-cycle regimes. Inhomogeneous hardening zone (IHZ) and un-melted TiC zone (UMTZ) resulting from TiC agglomeration, along with pore and lack of fusion (LOF) generated during the L-PBF process, play a crucial role in inducing fatigue failure and influencing the variability of fatigue life. Advanced microscopy techniques, including optical microscopy, scanning electron microscopy, and electron backscatter diffraction, were employed to elucidate four failure modes: LOF-assisted IHZ cracking, IHZ cracking, pore cracking, and UMTZ cracking. IHZ cracking originates from stress concentration caused by the mechanical property mismatch between IHZ and Ti matrix, leading to brittle fracture of α'-grains within the IHZ. This constitutes the predominant failure mode. The presence of LOF near IHZ further exacerbates stress concentration, diminishing the material's load-carrying capacity and significantly reducing fatigue life. Considering the fatigue cracking mechanism, microstructural characteristics and the influence of defect location and stress concentration, a crack nucleation life prediction model is developed. The agreement between experimental and predicted data is satisfactory.

Microstructure and Mechanical Properties of A6061/GA980 Resistance Spot Weld

Resistance spot welding was performed on steel and an Al alloy to investigate the microstructural and mechanical properties of the joint. An Al-Mg-Si aluminum alloy A6061 and an alloyed zinc-plated steel sheet GA980 were used as specimens. Resistance spot welding was performed at welding currents of 16 kA, 20 kA, and 22 kA, welding time of 0.24 s, and welding pressure of 5 kN. To investigate the strength of the welds, the tensile shear test and the cross tension test were conducted, and the fatigue test was also conducted. The nugget diameter increased with an increase in the welding current. The tensile shear strength and cross tension strength increased with the increase in the welding current. In the tensile shear fatigue test, interface fracture was observed in the low cycle fatigue region. In the cross tension fatigue test, it was confirmed that the higher the welding current, the better the fatigue properties in the low-cycle fatigue region.

High cycle fatigue properties of high-nitrogen steel hot-rolled with the yield strength level of 1000 MPa

The fatigue properties of an Fe-19Cr-20Mn-0.6N high-nitrogen steel (HNS), which was hot-rolled with the yield strength level of 1000 MPa, were investigated by means of tension–tension fatigue tests. The results showed that the fatigue life increased in a power law manner with the decrease of the maximum stress from 1040 MPa to 880 MPa. The fatigue limit at the 107 cycles was about 840 MPa, with the ratios of the fatigue limit to yield strength and tensile strength being 0.79 and 0.69, respectively. The high fatigue limit could be attributed to its high yield strength level, which was resulted from the mixed microstructure consisting of ultrafine grains and elongated grains with some slip bands.

Experimental Evaluation of Fatigue Properties of Carbon Fiber/Epoxy Matrix Interface and Numerical Simulation of Transverse Cracking under Cyclic Load

This study aims to experimentally evaluate the relationships between the interfacial tensile stress applied to the carbon fiber/epoxy matrix and the number of applied loading cycles when interfacial debonding is initiated. Tension – tension fatigue tests of single carbon fiber embedded specimens were performed, and digital image correlation observations were conducted during the fatigue tests. Changes in the microscopic apparent strain distribution during fatigue tests were utilized to detect the initiation of fiber/matrix interfacial debonding. The results demonstrated that the fiber/matrix interfacial tensile strength degraded depending on cyclic loading. Fatigue crack growth simulation was also performed based on the finite element method considering the strength degradation of the fiber/matrix interface.

Temperature-Moisture-Mechanical coupling fatigue behaviours of screwed Composite-Steel joints

This paper seeks to probe temperature-moisture-mechanical coupling fatigue behaviours of screwed composite-steel joints by using experimental and numerical methods. Novel temperature-moisture-mechanical (TMM) coupling constitutive model, fatigue failure criterion and progressive fatigue damage algorithm (PFDA) are first devised for simulating fatigue failure mechanisms and modes and for predicting fatigue lives of single-lap screwed composite-metal joints (CMJs) in arbitrary temperature-moisture environment. In order to validate the presented model and algorithm, tension–tension fatigue tests are then conducted on the CMJs in four representative environments: low temperature of −40 °C and dry (LTD), room temperature of + 23 °C and dry (RTD), room temperature of + 23 °C and wet (RTW) and elevated temperature of + 55 °C and wet (ETW), respectively. Finally, the TMM coupling fatigue behaviors of the CMJs are analyzed and discussed from the experiments and progressive fatigue damage modelling, and predicted results agree well with experimental findings, demonstrating the feasible and practical usage of the proposed model.

Investigation of Electromechanical Reliability and Radio Frequency Performance of a Highly Stretchable Liquid Metal Conductor for Wearable Electronics

Abstract Liquid metal-based gallium conductors exhibit unique physical and electromechanical properties, which make them excellent candidates for the next generation of wearable electronics. In this study, a novel fluid phase-based gallium conductor was stencil printed on thermoplastic polyurethane (TPU) to fabricate a stretchable conductor as well as a stretchable radio frequency (RF) transmission line. The electromechanical reliability of the conductor during high elongation as well as cyclic tension and bend fatigue was evaluated and compared with commercially available stretchable silver-filled polymer paste. The microstructure of the liquid metal conductor and the silver paste was investigated via scanning electron microscopy (SEM) before and after the samples were subjected to high elongation (>100%). Unlike the silver paste, the liquid metal conductor maintained its microstructural integrity while its resistance showed a linear response to changes in length. A cyclic tension fatigue test confirmed the fatigue-free performance of the liquid metal conductor during 8000 stretching cycles at a strain amplitude of 30%. The electromagnetic structure of the RF transmission line was simulated and then compared to the measured data. The measurements for insertion loss showed that U-bending, 90 deg twisting, and 1000 stretching cycles at a strain amplitude of 100% did not have a significant impact on the RF performance. Details of the DC tests and RF measurements, including the microstructural analysis and simulation results, will be discussed in this article.

Experimental and numerical investigations on the micro-damage behaviour of glass fibre-reinforced plastics

The formation and influence of micro-damage in glass fibre-reinforced plastics (GFRP) is carried out by numerical and experimental investigations. A quasi-static material characterisation is performed and the stiffness and strength of unidirectional, undamaged material in longitudinal and transverse direction as well as in the 23-plane are determined. Since the desired micro-damage could not be generated in unidirectional laminates due to abrupt failure, a [0∘/90∘]s layup has been identified to be most suitable to generate micro-damage in a reproducible way in the 90° layers, which is done using a tension–tension fatigue test program. During these experiments, micro-damage is detected optically and by means of ultrasonic birefringence, where the latter method shows a reduction in shear modulus due to fibre–matrix debonding prior to final inter-fibre failure. The shear modulus degradation is indirectly measured by the change in the velocity of sound. Since this method is limited to measurements in the 13- and 23-plane, all experiments are accompanied with microstructural simulations with detailed statistical volume elements (SVE), to study the influence of micro-damage under various loading conditions and directions. For loading in fibre direction, no influence on the mechanical properties is observed for the investigated fibre–matrix debonding. However, this is different for transverse loading, where a transverse shear stiffness loss of around 8% results in a decrease of transversal stiffness of around 18%, if the load direction is perpendicular to the damage plane. A similar behaviour is observed for the strength, which is reduced by a factor of 2 for the same configuration.

High cycle and very high cycle fatigue properties and microscopic crack growth modeling of Ti‐6.5Al‐3.5Mo‐1.5Zr‐0.3Si titanium alloy at elevated temperatures

AbstractPulsating tension fatigue tests were conducted at 25°C, 150°C, and 250°C to investigate the effect of temperature on high cycle and very high cycle fatigue behavior of titanium alloy. The fatigue strength decreases with the increase of temperature, and the surface failure is more sensitive to temperature than interior failure. Afterwards, the fatigue fracture morphology, microstructure, and texture of titanium alloy were characterized. The results show that the fracture of larger αp phase with the maximum shear stress and higher strain concentration is responsible for the facet formation. The formation of facets leads to the interior failure at different temperatures. Finally, combining with the definition of interior crack growth rate, an assessment approach was proposed to predict the crack growth rate within the inhomogeneous microstructure area (IMA), which takes crack growth acceleration caused by the increase of temperature into consideration.

Uniaxial Tension Fatigue Test of Asphalt Concrete—An Improved Framework

Abstract The stress and strain distributions in the uniaxial tension fatigue test are homogeneous and are better estimated than in the beam fatigue test. This condition is of utmost importance when analyzing the test using viscoelastic continuum damage (VECD). The uniaxial tension is nowadays conducted using crosshead displacement control. The strain control condition is difficult to realize with crosshead control. The paper proposes to use two extensometers with an averaging cable to control the strain in the central part of the specimen in the same manner as the load cell is used to control the stress and avoid the problems caused by the crosshead displacement control. The fatigue test history contains millions of data points and poses some difficulties in using the full-time history in the analysis of the test. It is proposed to conduct dynamic modulus and uniaxial tension fatigue tests on the same specimen and to implement numerical integration that reduces the computation effort. The analysis of two fatigue tests suggests that, with the full-time history, it is possible to: (1) Obtain an additional damage parameter, in addition to the maximum pseudo stiffness (PS). The maximum PS is calculated from the peaks of the stress and pseudo strain and represents the material state at the peak loading condition and at failure. The slope PS is calculated at beginning of the loading as the ratio of the damaged and undamaged moduli. It represents the material state at the end of the loading cycle; and (2) To make a more accurate estimation of the internal variable S which may be used as a material performance parameter.

Microstructural analysis of fine-grained magnesium after cyclic tension–tension fatigue testing at 0 °C

Microstructures were characterized for the fine-grained magnesium samples that experienced tension–tension fatigue testing and quasi-static tensile testing at 0 °C. Three fatigue cases were selected based on the relation between the maximum loading stress (σmax) of fatigue testing and the material's yield strength (σy). σmax was lower than σy for the first case, about equal to σy for the second case, and higher than σy for the third case. No tensile twinning was observed in the tested samples. With the increase of σmax experienced by the material, the number of small grains decreased and the number of large grains increased in the tested samples. Average grain size became larger for the samples after testing, and it increased linearly with the increase of σmax. Grain growth began with the merging of the blocks of small grains and continued with the merging of small grains to the neighboring large grains through grain rotation when σmax was increased.

Fatigue Resistance of a BFRP-Encapsulated Long-Gauge FBG Strain Sensor under Cyclic Train Loads

To verify the performance of a basalt fiber reinforced polymer (BFRP) fiber-encapsulated long-gauge strain sensor in railway bridge health monitoring, this paper studies the fatigue resistance and durability of the BFRP fiber-encapsulated FBG sensor under train loads. First, the influences of the length of the anchorage section and the length ratio of the sensing section on the accuracy of the sensor were studied. Then, the BFRP sensor was applied to a sleeper for 2 million cycles of tension fatigue testing. The strain-time history of the whole fatigue test was monitored and compared. After the test, a calibration test was carried out to verify the accuracy and repeatability of the sensor. Finally, the slip and fatigue cracking of the fiber in the anchorage section of the sensor were observed by electron microscopy. The results show that the gap between the anchoring section and the bare optical fiber was filled with epoxy resin, and there was no slip behavior. No fatigue cracking occurred in the fiber, and the strain coefficient and linearity of the sensor showed no obvious changes after 2 million cycles of loading. The long-gauge strain sensor encapsulated by BFRP fibers exhibited good fatigue resistance and can meet long-term monitoring requirements under train loads.

Probabilistic fatigue life prediction model of natural rubber components based on the expanded sample data

A novel method for determine the probabilistic distribution model of natural rubber (NR) fatigue life is proposed. Uniaxial tension fatigue tests are carried out on dumbbell-shaped cylindrical specimens. According to the fatigue test data, a support vector machine (SVM) model is established, in which the empirical reliability and the rubber fatigue life are considered as input and output variables, respectively. The SVM model is used to expand the NR fatigue life data. The analysis of the expanded data demonstrates that the NR fatigue life follows a lognormal distribution. Accordingly, the fatigue reliability evaluation of NR components is carried out.

Mechanical performance according to fiber lamination pattern for radar mast application

As the IMO has strengthened its environmental regulations to increase the energy efficiency of ships, the IMO has also begun to consider operational economics such as reducing energy consumption by reducing the weights of ships and their parts. This study conducts an analysis examining the application of a ship radar mast. The applicability of the laminated composite material was analyzed through tension, shear, compressive, and tension-tension fatigue tests and the FRP fatigue limit for one million cycles by the slope of the [Formula: see text]–[Formula: see text] curve was found to be about 231 MPa. It is expected that this method can be utilized in the design stage by predicting the fatigue life of radar masts for ships through fatigue testing.

Fatigue life prediction of natural rubber components using an artificial neural network

AbstractUniaxial tension fatigue tests conducted on dumbbell‐shaped specimens made of vulcanized natural rubber are carried out. Using the fatigue test data, a back‐propagation neural network (BPNN) model for estimating the fatigue life of natural rubber specimens is established. An improved sine‐cosine algorithm (ISCA) is proposed to optimize the parameters of the BPNN model. The peak engineering strain, ambient temperature, and Shore hardness of natural rubber specimens are used as the input variables while the rubber fatigue life as the output variable of the BPNN model. The regression results and predicted life distribution of the established BPNN model are encouraging. For comparison, a genetic algorithm, a particle swarm algorithm, and a standard sine‐cosine algorithm are also used to obtain the BPNN model parameters, respectively. The results showed that the prediction accuracy and efficiency of ISCA are better than other three algorithms. In addition, the sensitivity analysis is introduced to quantify the relative influence of the model inputs on the output.