Fatigue Characteristics Research Articles

Development of high performing hybrid hot mix asphalt mixtures

ABSTRACT In this study, mixture design volumetrics, moisture-induced damage and fatigue characteristics of hybrid hot mix asphalt (HMA) fabricated with crumb rubber (CRM) and polyvinyl alcohol (PVA) fibre were evaluated. Indirect tensile strength test was conducted to assess several tensile and fracture attributes of control, polymer-modified, CRM-modified, PVA-reinforced and hybrid HMA. Long-term performance of aged hybrid HMA was also assessed using flexural beam fatigue test. Comparison of mixture designs indicated a change in volumetric properties of hybrid mixture with acceptable resistance to stripping. Experimental results revealed that fracture energy and dissipated creep-strain energy of the HMA with 2%CRM and 0.2%PVA doubled relative to polymer-modified HMA. The developed hybrid HMA presented around 29 times higher resistance to repeated load failure with 90% reduction in crack propagation rate and over 12 times higher energy for unit crack propagation compared to conventional HMA. Additionally, effective fibre bridging across the crack and adequate coating of asphalt on CRM through image analysis revealed wider strain distribution, a perverse intricate fracture pattern and better adhesion. The higher fracture resistance, toughness indices, and resilience under repetitive traffic loading of hybrid mixtures could be effective in extending the service-life and enhancing long-term performance of flexible pavements.

Assessment of residual stresses in railway rails using ultrasonic and Barkhausen noise techniques

Residual stress, a factor affecting the fatigue and fracture characteristics of rails, is formed during the processes of fabrication and heat treatment, and is also generated by shrinkage/tension due to the temperature differences and vertical loads on wheels due to the weight of vehicles. Moreover, damage to rails tends to accelerate due to residual stress caused by the continuous increase in the number of passes and the high speed of passing vehicles. Because this can have a direct effect on safety accidents on railroad rails, having a technique to evaluate and analyse the residual stresses in rails accurately is very important. In this paper, firstly, residual stresses applied in rails were evaluated using longitudinal critically refracted (LCR) wave. Non-destructive stress measurement using ultrasonic techniques is based on calculation of the acoustoelastic coefficient obtained from the relationship between material stress and LCR wave velocity. This is because LCR waves exhibit a relatively large change in flight time in relation to a change in stress compared to other ultrasonic modes. Barkhausen noise technique is also very suitable for measuring residual stresses on railway rails, which are ferromagnetic materials. Tensile and compression tests were performed with the specimens extracted from the inspection object, and the difference between the ultrasonic speed and the magnetization amplitude according to the applied stress was measured. Then, the feasibility of calculating the internal stresses in railway rails using the reference data obtained from the extracted specimens was determined, and the reliability of each method was verified. Furthermore, based on these results, the difference in the results for the loads asymmetrically applied according to the wheel shape was analysed by measuring for each part of new and used rails.

A review on fracture and fatigue behaviour of FSW joints of Al alloys

Friction stir welding (FSW) is solid state welding process. In this process two similar or dissimilar metallic plates are join using appropriate heat and mechanical forces with the help of rotating tool. Due to mechanical advantages like high strength to weight ratio, aluminium (Al) alloys commonly used in several engineering prospective. Recently, FSW has gained consideration in the automobile, aerospace and marine industries owing various advantages, like high weld strength, low distortion and good fatigue behaviour. This study concentrates on the fracture and fatigue characteristics of Al alloy FSW joints and importance of optimizing FSW process characteristics such as tool rotational speed, travel speed and tool offset, to obtain best joints with improved mechanical properties. This review also highlights the effect of microstructure and residual stresses on the fracture and fatigue behaviour of FSW joints as well as it provides an overall understanding of the fracture and fatigue behaviour of FSW joints of Al alloys.

Comparison of deformation behavior between creep and fatigue on siltstone and its modified damage model

AbstractIn order to reveal the deformation behavior similarity between creep and fatigue, a series of creep and cyclic load tests were performed on siltstone under various load levels. First, the mechanical characteristics of creep and fatigue were compared, by analyzing the strength, ultimate strain, and steady deformation rate of siltstone. Then, a modified fatigue damage creep model was established by connecting a viscoplastic damage element in series with Burgers mode. Finally, the applicability of the model was verified, and the model parameters were analyzed. The results show that the fatigue failure of siltstone is controlled by fatigue strength and limit strain. The modified fatigue damage creep model can accurately describe the whole deformation process of siltstone under cyclic load test. Compared with creep test, the cyclic load hardly affects the elastic modulus of this model. However, the viscosity coefficient of this model is greatly weakened by the cyclic load.

Microstructure-based interior cracking mechanisms and life prediction of additively manufactured Ni-based superalloy with temperature effect

The localized microstructure related fatigue cracking of additively manufactured (AM) Ni-based superalloy has been attracting increasing attention. Understanding the connection between the inhomogeneous microstructure and the fatigue characteristics with small deformation is crucial. Herein, the microstructure-related high cycle fatigue and very high cycle fatigue properties of an Ni-based AM superalloy were examined. The fatigue tests were conducted with stress ratio of 0.1 at room (25 ℃) and elevated (650 ℃) temperatures. To support the modeling of the internal fatigue failure mechanism, additional studies on microstructure features and mechanical properties were carried out in conjunction with electron backscatter diffraction, energy dispersive spectrometry, and monotonic tensile tests. Results of 2D fracture surface observation showed that the interior facet-induced fatigue crack nucleated under relatively low applied stress at both temperatures, which were assisted by the interior abnormal structure. Furthermore, the interior crack nucleation region consisting many facets was formed under shear stress and strain based on 3D restructure of fracture surface. Combined with evaluation of threshold stress intensity factor, the transition lengths from small crack to long cracks for surface failure at 25 ℃ and interior failure at 650 ℃ were evaluated. Based on the above analysis, the interior failure mechanisms were summarized related with microstructure characteristics. Finally, fatigue index parameters based on different failure modes were calculated to predict the fatigue life. The anticipated and experimental data are determined to be in satisfactory agreement.

A comparison of two wave energy converters’ power performance and mooring fatigue characteristics – One WEC vs many WECs in a wave park with interaction effects

The production of renewable energy is key to satisfying the increasing demand for energy without further increasing pollution. Harnessing ocean energy from waves has attracted attention due to its high energy density. This study compares two generations of floating heaving point absorber WEC, WaveEL 3.0 and WaveEL 4.0, regarding their power performance and mooring line fatigue characteristics, which are essential in, e.g., LCoE calculations. The main differences between the two WECs are the principal dimensions and minor differences in their geometries. The DNV software SESAM was used for simulations and analyses of these WECs in terms of buoy heave motion resonances for maximising energy harvesting, motion characteristics, mooring line forces, fatigue of mooring lines, and hydrodynamic power production. The first part of the study presents results from simulations of unit WEC in the frequency domain and in the time domain for regular wave and irregular sea state conditions. A verification of the two WECs’ motion responses and axial mooring line forces is made against measurement data from a full-scale installation. In the second part of the study, the influence of interaction effects is investigated when the WECs are installed in wave parks. The wave park simulations used a fully-coupled non-linear method in SESAM that calculates the motions of the WECs and the mooring line forces simultaneously in the time domain. The amount of fatigue damage accumulated in the mooring lines was calculated using a relative tension-based fatigue analysis method and the rainflow counting method. Several factors that influence the power performance of the wave park and the accumulated fatigue damage of the mooring lines, for example, the WEC distance of the wave park, the sea state conditions, and the direction of incoming waves, are simulated and discussed. The study's main conclusion is that WaveEL 4.0, which has a longer tube than WaveEL 3.0, absorbs more hydrodynamic energy due to larger heave motions and more efficient power production. At the same time, the accumulated fatigue damage in the moorings is lower compared to WaveEL 3.0 if the distance between the WECs in the wave park is not too short. Its motions in the horizontal plane are larger, which may require a larger distance between the WEC units in a wave park to avoid losing efficiency due to hydrodynamic interaction effects.

FATIGUE CHARACTERISATION OF MARTIAN CONCRETE: A REVIEW

Spacecraft have been dispatched to Mars as part of human missions aimed at exploring new frontiers, driven by the observed similarities between the red planet and Earth. This endeavour has facilitated the development of construction materials suitable for human settlements on Mars. To determine the optimal properties for constructing habitable infrastructure for humans on Mars, research efforts have led to the discovery of Martian concrete, composed of sulphur and Martian simulants that had been produced without water, which is in scarce supply on Mars. By utilising egolith available near the construction site, structures can be built efficiently and rapidly, supporting the establishment of sustainable human habitats on Mars. Several studies have been conducted to address the challenges associated with identifying the ideal proportions of Martian concrete. Given the extreme and harsh conditions on Mars, there is a growing interest in understanding how the properties of Martian concrete can mitigate and alleviate fatigue resulting from the planet’s daily conditions, such as temperature variations and dusty storms, which impose cyclic loading on structures. Therefore, it is crucial to investigate the fatigue characteristics of Martian concrete. By evaluating the fatigue properties of Martian concrete, considering the selected appropriate mix design ratios, this study aims to contribute to understanding the impact of Martian conditions on construction practices. Ultimately, the findings of this study can assist future researchers in comprehending the effects of the Martian environment on the planet’s construction process.

Development and evaluation of the Norwegian Fatigue Characteristics and Interference Measure (FCIM) for stroke survivors: cognitive interviews and Rasch analysis

PurposeThere is need for a comprehensive measure of post-stroke fatigue with sound measurement properties. This study aimed to develop the Norwegian Fatigue Characteristics and Interference Measure (FCIM) and assess its content validity, structural validity, and internal consistency.MethodThis study consisted of three steps: (1) an expert panel developed version 1.0 of the Norwegian FCIM, (2) its content validity was assessed in cognitive interviews with stroke patients (N = 15), (3) a convenience sample of stroke patients (N = 169) completed an online questionnaire with the FCIM, Fatigue Severity Scale, and sociodemographic information; validity and reliability were assessed using Rasch analysis.ResultsFCIM version 1.0 included a 10-item characteristics subscale, a 20-item interference subscale, and two pre-stroke fatigue items. The cognitive interviews revealed content validity issues, resulting in two interference items being removed and five items being flagged but retained for Rasch analysis (version 2.0). Rasch analysis led to removal of four items from the characteristics subscale and six more from the interference subscale. The final six-item characteristics subscale and 12-item interference subscale (version 3.0) both showed adequate fit to the Rasch model with indications of unidimensionality and local independence. The interference subscale had a high person separation index. No significant differential item function (DIF) was found in relation to gender, but one item demonstrated DIF in relation to age.ConclusionThe cognitive interviews and Rasch analysis demonstrated that the Norwegian version of the FCIM has high content validity, structural validity, and internal consistency. Future research should assess its construct validity, reliability, and responsiveness.

Review of the surface treatment process for the adhesive matrix of composite materials

To deepen the research on the surface treatment technology of bonding matrix of composite materials, carbon fiber reinforced polymer (CFRP) was selected as the research object, and the research status at home and abroad were reviewed from three aspects: matrix characteristics, durability and bonding and stripping effect before and after surface treatment. Because of the effects of existing surface treatments on the surface roughness, surface wettability, surface morphology, fatigue characteristics, shear strength, and tensile section morphology of CFRP, the influence mechanism of surface treatments on the bonding properties of CFRP was summarized, and the future research focus and direction prospected. The results show that the bonding effect depends on the good mechanical interlocking and adsorption/chemical bonding between the adhesive and CFRP surface. The surface treatment can remove the surface pollutants of CFRP, optimize the surface topography characteristics, and enhance the spreading ability of the adhesive on the substrate surface, thereby enhancing the bonding ability between CFRP and the adhesive. The combination of different surface treatments can significantly improve the preparation quality of the CFRP surface, and avoid the defects of the single surface treatment itself to a certain extent. The surface treatment technology of the bonding matrix is developing in the direction of precision, refinement, and accuracy.

A New Ensemble Prediction Method for Reclaimed Asphalt Pavement (RAP) Mixtures Containing Different Constituents

Fatigue and rutting are two common damage types in asphalt pavements. Reclaimed asphalt pavement (RAP), as a sustainable approach in the pavement industry, deals with the foregoing damage. Fatigue and rutting characteristics of asphalt pavement are generally assessed using laboratory tests, taking a long time and consuming significant amounts of raw material. This study aims to propose a novel approach for predicting fatigue and rutting performance of RAP mixtures. A new ensemble prediction method, named COA-KNN, is introduced by combining the coyote optimization algorithm and K-nearest neighbor to increase the accuracy of fatigue and rutting prediction. In order to evaluate the accuracy, the proposed method was compared against robust prediction methods, including random forest (RF), gradient boosting (GB), decision tree regression (DT), and multiple linear regression (MLR). Afterward, the influence of each variable on the mentioned damages is examined, and the variables are ranked based on their relative influence on the mentioned damages. The results suggest that COA-KNN outperformed other prediction techniques when comparing different performance indicators. Total binder content in asphalt mixes and the PG span of the virgin binder added to the recycled asphalt mixture had the highest relative influence on fatigue and rutting performance, respectively.

Fatigue Strength Evaluation of Cu–Ni–Si Alloy Strips

Abstract This study investigates the mean stress effect on the fatigue strength and the mean stress effect criterion that best represents this effect in Cu–Ni–Si alloy strips using a new test method. Since the cyclic bending fatigue test based on the fatigue test standard for Japan Copper and Brass Association for understanding the fatigue characteristics of Cu–Ni–Si alloy strips needs many test times, a new test method to conduct effectively was examined and developed, and after confirming its validity, the mean stress effect criterion was identified using this method. The effect of surface electroplating on fatigue properties was also investigated. As a result, it was confirmed that the mean stress effect criterion on the fatigue strength of Cu–Si–Ni alloy strips was represented well by the elliptic line. The effect of surface electrolytic plating on fatigue properties was found to be strongly influenced by surface roughness rather than Young’s modulus or hardness of the constituent plating.

A method for studying the frequency stability of materials during tests for multi-cycle fatigue of steel

For trouble-free operation without loss of elastic and inelastic properties of particularly critical elements of electrical-to-mechanical vibration converters during a long period of cyclic operation, it is necessary, in addition to studying the fatigue characteristics of materials used for their manufacture, to study these alloys for frequency stability, since minor deviations in the frequency of natural oscillations lead to unacceptable errors in the operation of such high-precision products. To carry out such studies, we developed and constructed an original installation, in which sinusoidal loading is carried out according to the “soft” scheme of flat samples cantilever bending operating in self-oscillation mode. The frequency of cyclic loading in this installation is generated by current pulses, which are a response to the frequency of the test sample natural oscillations converted using electronics. As a result, frequency equality is achieved in the test process. An algorithm for calculating stresses depending on the loading amplitude of steel samples of different geometric shapes was developed. It is shown that the stress on the sample calculated by the deformation amplitude in all cases is 8 – 10 % higher than the stress calculated by the force, regardless of the shape of the proposed samples. To verify the proposed research method, martensitic-aging steel was tested at loads close to the fatigue limit, since frequency stability in this range is of great interest. We obtained the frequency characteristics in the multi-cycle test area. It was determined that with an operating time of 50 million loading cycles, the frequency change was 0.75 Hz. The dynamics of frequency stability was revealed: the frequency changed most intensively during the first 10 million loading cycles, during this time the frequency changed by 0.54 Hz.

Study on Fatigue Characteristics of Rivets in Bearing Cage for an Aeroengine Transmission System

This study focuses on the rivet early fatigue characteristics in a deep-groove ball bearing cage for a transmission system in a turboprop engine. Nonlinear dynamic differential equations for the deep-groove ball bearing with a two-piece cage were developed. The rivet stress was used to identify the early failure mechanism of the rivets. This investigation revealed that by delivering an optimal preload of the rivet causes the two halves of the cage have less misalignment and a lower rivet stress. The fit relationship between the rivet and the rivet bore has a significant influence on the rivet stress. Excessive clearance increases the stress on the head of the rivet, while excessive interference increases the stress on the middle of the rivet. For the 1.5 mm diameter rivet analyzed in this study, the appropriate fit relationship is −0.02 mm–0 mm. A reasonable matching value of the load and the speed and the cage clearance ratio are beneficial to reducing the rivet stress. The impact load acting on the bearing and a ring misalignment can increase the rivet stress.

Nickel metal matrix composites reinforced with solid lubricants: A comprehensive review

Nickel metal matrix composites are suitable for aerospace and military applications due to their superior mechanical and tribological properties. The incorporation of reinforcing components in the nickel metal matrix composites significantly improves the specific strength, microhardness, wear resistance, frictional behavior, creep, and fatigue characteristics, as well as provides exceptional surface quality in comparison to typical engineering materials. The current study attempted to explore a review on nickel composites reinforced with various solid lubricants, along with their pros and cons. The study focuses on the issues like interfacial transition, agglomerating activity, and non-uniform particle dispersion. Several studies have been conducted to highlight the effect of solid lubricants on the microstructure, mechanical and tribological characteristics such as tensile strength, yield strength, ductility, hardness, friction, wear, and fatigue. In this review, the principal applications of various nickel matrix composites are also thoroughly examined.

Finite element analysis of bevel gear tooth side clearance and fatigue characteristics under alternating torque

In this paper, the effect of different tooth side clearances on the fatigue characteristics of bevel gears under alternating torque is investigated using finite element analysis technology. The article first determines the structure form and main parameters of the bevel gear and completes the establishment of the three-dimensional model of bevel gear transmission. Then, based on the principle of finite element analysis, the fatigue characteristics of the bevel gear under different tooth side clearances are simulated by ANSYS workbench software. Next, according to the simulation results, the changes in service life and safety coefficient of bevel gear with tooth side clearances are analyzed, and the relevant conclusions are drawn. Finally, combined with the finite element analysis results, the axial adjustment amount of the bevel gear assembly of this project is guided, and the actual use effect is verified. The results show that when the tooth side clearance jn is taken in the range of 0.04·m∼0.08·m, the fatigue safety coefficient and service life of bevel gear gradually decrease with the increase of tooth side clearance jn.

Study on mechanical and micro-structural properties of aluminium matrix composite reinforced with graphite and granite fillers

Composites are gaining increasing popularity nowadays due to their wide range of applications and flexible design options. Aluminium Matrix Composites (AMCs) have garnered increasing attention in contemporary times as a subject of research. The inclusion of reinforcements in the metallic matrix results in improved stiffness, specific strength, wear resistance, creep resistance, and fatigue characteristics when compared to conventional engineering materials. In our study, we are employing a 6061 grade Aluminium alloy as the fundamental material, and augmenting it with Synthetic Graphite and Granite fine particles as strengthening agents. The Aluminium matrix composite is produced through the incorporation of synthetic graphite particles and granite dust into the molten aluminium via a Stir Casting Furnace utilising a bottom pouring technique at temperatures within the range of 850 to 950 °C. The Aluminium Metal Matrix composite samples is fabricated with varying reinforcement percentages relative to the base material. The distribution of particles within the Aluminium Matrix is analysed. Furthermore, the fabricated composites have undergone Tensile, Impact, Shear, and Micro hardness tests to assess the effects of incorporating reinforcements. All examinations conform to the standards set by ASTM. A comparative analysis is conducted between the mechanical properties exhibited by the original Aluminium alloy and the Aluminium metal matrix composites that have been manufactured.

Study of fatigue characteristics of key welds of modular drilling derricks

Driven by the gradual development of oil and natural gas resources, the global use of rigs and the number of wells rise steadily. Modular rigs play an important role in oil exploration because of their efficient transport, economy, technological advancement, and rig reliability. The derrick is a key part of the modular rig, and since many essential components in the derrick are welded, the fatigue life of the derrick weld is particularly relevant. In this paper, the modular rig is the object of the research, proposing the calculation formula of fatigue life of the key weld of the derrick. Using modular rig ZJ90D as an example, and combining the rig working conditions with the structural characteristics of the derrick, the key calculation parameters are obtained by numerical analysis. Thus, the life expectancy of the key weld is calculated according to the calculation formula of fatigue life presented herein. The research results have important reference significance and guiding value for the design and optimization of modular rig derricks.

Kaji Eksperimental Karakteristik Fatik Komposit Polyester Partikulat Al2O3

This research investigates the fatigue characteristics of Al2O3 particulate polyester composite, including fatigue limit, fatigue life, and fracture surface morphology in the test specimens. Fatigue test specimens with variations of Al2O3 filler of 4%, 6%, 8%, and 10% were tested using a rotary bending fatigue testing machine under varying loads to determine the number of cycles until failure. The research results indicate that the polyester composite with 4% and 6% Al2O3 filler had a fatigue limit of 1.9 MPa and could withstand 1.000.000 cycles. Meanwhile, the polyester composite with 8% and 10% Al2O3 filler had a fatigue limit of 0.9 MPa and also endured 1.000.000 cycles. The average fatigue life was 28.957 cycles, 22.725 cycles, 98.572 cycles and 66.352.5 cycles for 4% mass fraction, 6% mass fraction, 8% mass fraction, and 10% mass fraction respectively. The fracture surface morphology of the test specimens varied significantly, mainly due to multiple origins, where multiple initiation points of fracture simultaneously occurred, leading to surface erosion or tearing before the specimen ultimately failed or fractured.

Impacts of nano-clay particles and heat-treating on out-of-phase thermo-mechanical fatigue characteristics in piston aluminum-silicon alloys

Abstract. In this article, the effect of nano-clay particles and heat-treating on thermo-mechanical fatigue (TMF) behaviors and failures of piston aluminum-silicon (AlSi) alloys was investigated. For this purpose, thermo-mechanical fatigue tests were conducted under out-of-phase (OP) loading conditions. Two loading conditions were checked based on different maximum temperatures (250, 300, and 350 °C) and various thermo-mechanical loading factors (100, 125, and 150%). The minimum temperature was constant in all tests at 50 °C under a heating/cooling rate of 10 °C/s and a dwell time of 5 s. Results showed that the nano-composites had a longer fatigue lifetime, at least 2 times higher, compared to the Al alloy, when the maximum temperature was 250 °C and the thermo-mechanical loading factor was 100%. However, no effective change was seen for the stress value and the plastic strain. At higher maximum temperatures, the change in the material behavior was lower. The fracture analysis by scanning electron microscopy (SEM) demonstrated that both materials had a brittle behavior due to cleavage and quasi-cleavage marks. The damage mechanism was also due to the Si-rich phase and intermetallics, respectively for the crack propagation and the micro-crack initiation.

Influence of Silicon Carbide and Graphite Reinforcements and T6 Aging Heat Treatment on the Fatigue Characteristics of AZ91D Magnesium Alloy

Influence of Silicon Carbide and Graphite Reinforcements and T6 Aging Heat Treatment on the Fatigue Characteristics of AZ91D Magnesium Alloy