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Background: Efficient biaxial strain control to study fatigue damage growth in composite materials at the coupon scale level under realistic multi-axial stress states observed in structures is needed. Objective: Two biaxial cyclic strain control algorithms, referred to here as the active and the passive control method, are presented as a fatigue testing strategy for composite materials. Method: The strain is measured at a sampling frequency of 116 Hz through a real-time digital image point tracking system. The active control method utilizes a cascade control algorithm to accommodate the low sampling rate of the digital image point tracking system relative to the servo-hydraulic PID controller. The passive control method is a conditional control algorithm where the force command is adjusted when the measured peak-valley strain violates the predefined strain tolerance. The performance of these control techniques are initially evaluated on uniaxial coupon specimens to investigate the effect of testing frequency, strain magnitude, accuracy of the stiffness parameter and the tolerance band. Subsequently, the two control methods are verified on cruciform specimens under different biaxial strain states. Results: Under biaxial loading, the peak feedback strains had a maximum error of 6.4% and 9.0% for the active and the passive control method respectively, depending on the required biaxial strain state. Conclusions: The active control method was found to offer a better accuracy relative to the passive control method. However, it suffered from a lower fidelity as the test stopped whenever the real-time digital image point tracking system lost track of the point markers. [ABSTRACT FROM AUTHOR]

The high cycle fatigue behaviour of autoclave-cured carbon fibre-reinforced polymer (CFRP) composite gears is investigated. The CFRP gears were milled from a composite plate and tested in mesh with a steel drive gear under five torque loads ranging between 0.4 and 0.8 Nm in unlubricated conditions. A detailed gear damage analysis is conducted by employing scanning electron microscopy and high-resolution optical microscopy. Epoxy matrix microcracking is found to be the damage mechanism that leads to the final delamination failure. CFRP gears exhibited a significantly improved performance and a longer fatigue lifespan in comparison with the polymer and polymer composite gears.

Purpose: To investigate the effect of core dental implant materials supporting single crowns on the probability of survival and failure modes. Materials and Methods: Thirty-six standard external-hex titanium implants (4.0 mm In diameter) were selected to restore single crowns and divided into two groups according to core material: commercially pure grade 2 titanium (G2) and grade 5 titanium-aluminum-vanadium alloy (Ti-6AI4V) (G5). Abutments were screwed to the implants, and standardized maxillary central incisor metal crowns were cemented and subjected to step-stress accelerated life testing in water. Use-level probability Weibull curves and reliability for missions of 100,000 cycles at 150 N and 200 N (with 90% two-sided confidence intervals [CIs]) were calculated. Polarized light and scanning electron microscopes were used to determine the failure modes. Results: Use-level probability Weibull calculations showed beta values of 0.59 (Cl, 0.31 to 1.11) and 1.22 (Cl 0.81 to 1.84) for G2 and G5, respectively, and significantly higher characteristic strength and Weibull modulus for G5. The calculated reliability (90% CIs) for a mission of 100,000 cycles at 150 N showed that cumulative damage would lead to survival of 45% of implant-supported crowns of G2 and 98% of G5. At 200 N the probability of survival decreased to 0.03% for G2 and 21% for G5. Abutment screw fracture was the failure mode for all groups. Conclusion: Reliability, characteristic strength, and Weibull modulus were significantly higher for Ti-6AI-4V dental implants than for commercially pure (grade 2) titanium implants. Failure modes were similar for both groups. [ABSTRACT FROM AUTHOR]

The manufacturing of case-hardened gears usually consists of several complex and expensive steps to ensure high load carrying capacity. The load carrying capacity for the main fatigue failure modes pitting and tooth root breakage can be increased significantly by increasing the near surface compressive residual stresses. In earlier publications, different shear cutting techniques, the near-net-shape-blanking processes (NNSBP's), were investigated regarding a favorable residual stress state. The influence of the process parameters on the amount of clean cut, surface roughness, hardness and residual stresses was investigated. Furthermore, fatigue bending tests were carried out using C-shaped specimens. This paper reports about involute gears that are manufactured by fineblanking. This NNSBP was identified as suitable based on the previous research, because it led to a high amount of clean cut and favorable residual stresses. For the fineblanked gears of S355MC (1.0976), the die edge radii were varied and the effects on the cut surface geometry, hardness distribution, surface roughness and residual stresses are investigated. The accuracy of blanking the gear geometry is measured, and the tooth root bending strength is determined in a pulsating test rig according to standardized testing methods. It is shown that it is possible to manufacture gears by fineblanking with a high precision comparable to gear hobbing. Additionally, the cut surface properties lead to an increased tooth root bending strength. [ABSTRACT FROM AUTHOR]

Fatigue cracks have appeared as a significant issue for joints and connections in existing steel structures in the last decades. Therefore, those are a major inspection and maintenance matter for any steel structure's operator. This emphasises the importance of using a reliable detection method to determine the crack size and assessing the severity of such a crack on the structural integrity of a structure. In this article, the effectiveness of strain measurement in detecting fatigue cracks in transversal non‐load carrying welded attachment subjected to out of plane axial loading is studied. Numerical analysis and experimental investigations allowed to correlate the decrease in strain measured by attached gauges to the crack depth at the weld toe. In addition, different strain evolution patterns were found during fatigue testing, and the fracture surfaces of the specimens were observed to interpret these patterns. Moreover, the crack position with respect to the weld toe surface was predicted via strain measurements. [ABSTRACT FROM AUTHOR]

Stereo‐digital image correlation (SDIC) is used for the analysis and quantification of parasite bending stresses in a fatigue specimen due to its mounting in a misaligned load frame. The aim of this work is to provide an easy way to estimate the induced parasite bending stresses due to the load frame misalignment, using the out‐of‐plane displacement measurements obtained by SDIC and beam theory. Analytical solutions of parasite stresses as a function of out‐of‐plane misalignments are provided for flat fatigue specimens having (a) tangentially blending fillets between the uniform test section and the ends and (b) continuous radius between the ends. Simple procedures for aligning a commercial load frame in accordance with international standards are also provided. The bending stresses profile along the specimen main axis obtained by numerical simulations have shown a very good agreement with the results obtained by the analytical models. The proposed methodology could complement standard alignment techniques based on samples instrumented with strain gauges or, in their absence, even replace established procedures. [ABSTRACT FROM AUTHOR]

Kirschner wires (K wires) are a common fixation device in foot and ankle surgery, particularly in lesser-toe fixation. Fatigue failure is a known complication of this fixation. The material properties of the K wire are a factor in the strength and durability of the wire. The purpose of this study is to compare the durability of K wires made of stainless steel, titanium, and Nitinol. Ten samples each of stainless steel, titanium. and Nitinol underwent cyclic durability testing using a rotating beam approach, and S-N curves (applied stress vs the number of cycles to failure) were generated. The results demonstrate that, generally, Nitinol K wires have a shorter life for the same applied stress than the stainless steel or titanium wires. Titanium had a longer life at low stresses compared with stainless steel, and stainless steel had a longer life at higher stresses. This study provides comparative durability data for K wires made of different metals, which have not been previously reported. Although there was a statistically significant difference in durability for wires used in K wire fixation, all 3 metal types are reasonable choices for temporary K wire fixation. Levels of Evidence: Level 5: Mechanical study [ABSTRACT FROM AUTHOR]

In the aerospace industry, spacecraft often serve in harsh operating environments, so the design of ultra-lightweight and high-performance structures is a major requirement in aerospace structure design. In this article, a lightweight aerospace bracket considering fatigue performance was designed by topology optimization and manufactured by 3D-printing. Considering the requirements of assembly with a fixture for fatigue testing and avoiding stress concentration, a reconstructed model was presented by CAD software before manufacturing. To improve the fatigue performance of the structure, this article proposes the design idea of abstracting the practiced working condition of the bracket subjected to cycle loads in the vertical direction via a multiple load-case topology optimization problem by minimizing compliance under a variety of asymmetric extreme loading conditions. Parameter sweeping was used to improve the computational efficiency. The mass of the new bracket was reduced by 37% compared to the original structure. Both numerical simulation and the fatigue test were implemented to support the validity of the new bracket. This work indicates that the integration of the proposed topology optimization design method and additive manufacturing can be a powerful tool for the design of lightweight structures considering fatigue performance. [ABSTRACT FROM AUTHOR]

3D-printed Ti-6Al-4V materials can be used for implantation upon the confirmation of medical device specifications. Moreover, Young's coefficient of porous Ti-6Al-4V is close to that of the human bone, and it can allow the growth of bone cells through holes to fuse with implant materials. In this study, porous Ti-6Al-4V samples were fabricated by 3D printing. The fabricated porous Ti-6Al-4V samples had four rows of holes in the front and one or two rows of holes in the side. The mechanical properties and fatigue lifetimes of the porous Ti-6Al-4V samples were analyzed, where the samples were prepared by selective laser melting (SLM) 3D printing followed by post-heat treatment at a temperature of 500, 700, or 925 °C in a vertical tube furnace for 2 h with a heating rate of 10 °C/min. A tensile testing machine was used to measure Young's modulus and tensile strength of the porous Ti-6Al-4V alloy samples. Upon microstructural observation by SEM, the as-fabricated 3D-printed sample showed a fine needlelike martensite structure, and the 500- and 700-°C-treated samples showed a needle-like ß-structure. Additionally, the 925-°C-treated sample showed a coarse ß-structure. The porous Ti-6Al-4V sample subjected to post-heat treatment at 500°C had the lowest Young's modulus and the highest tensile strength, where the strengths used in the fatigue testing were 0.1, 0.2, and 0.6 times the yield strength. The fatigue lifetimes of the porous Ti-6Al-4V samples with one and two rows of holes in the lateral side were 128941 and 22721 cycles at 0.2 times the yield strength, respectively. [ABSTRACT FROM AUTHOR]

Pavement maintenance and rehabilitation is as much important as the construction work itself. In this scope, applying the correct and efficient repair method is highly critical for economic and technical reasons. Depending on the damage level, many alternative repair methods exist. Using an overlay is one common method, where a new layer can be directly applied over or replace the top part of an existing pavement. This overlay can be made from asphalt or concrete as well. With the advances in the concrete technology, the long service life of concrete pavements compared to asphalt let this overlay gains importance recently. Yet, the rigid nature of concrete requires a high thickness for an overlay. In this work, Engineered Cementitious Composite (ECC) type of concrete was suggested to be used as an overlay considering its ability, with a less thickness, to reduce the reflection of the cracks from the old pavement. To testify this property, the performance of two ECC mixtures as a concrete pavement overlay was investigated under fatigue loading. Using Weibull distribution, the failure probability of these mixtures was determined, and it was shown that the mineral admixture type utilized significantly affects the fatigue performance of ECC. [ABSTRACT FROM AUTHOR]

Objective: To investigate the probability of survival and failure modes of four‐unit implant‐supported porcelain fused to metal (PFM) dentogingival prostheses subjected to step‐stress accelerated life testing (SSALT). Materials and methods: Eighteen implant‐supported PFM dentogingival prostheses with thin metallic infrastructures, which provided minimal ceramic support and improved esthetics were fabricated over external hexagonal connection UCLA abutments. SSALT was performed until specimen failure. Use level probability Weibull curve and reliability were calculated and plotted. Weibull modulus (m) and characteristic strength (η) were also calculated. Polarized light microscope and scanning electron microscope were used to characterize fractures. Results: Failures were dictated by material strength rather than fatigue damage accumulation. The probability of survival for loads reaching 100 and 150 N in 100,000 cycles was 92 and 61%, respectively. No cracks or fractures were identified in the veneered porcelain, whereas abutment fixation screw fracture was the chief failure mode. Conclusion: Implant‐supported PFM four‐unit dentogingival prostheses with minimum metal framework dimensions presented favorable lifetime prediction under fatigue testing. Fractures were restricted to fixation screws. Clinical significance: In‐vitro fatigue testing and failure mode analyses evidenced favorable lifetime prediction for 4‐unit implant‐supported dentogingival prostheses with minimum metal frameworks. Abutment fixation screw fracture might be the most frequent clinical complication. Since this proof of concept has been tested in‐vitro, further studies including different restorative materials, as well as long‐term clinical trials are warranted. [ABSTRACT FROM AUTHOR]

This article describes how a step‐stress accelerated life test (SSALT) can be designed for testing the fatigue life and reliability of structural components with a dominant failure mode. With simple numerical simulations of the crack's propagation in the notched area of the structural part for different loading levels, the slope of the S–N curve for a structural component is initially estimated. Then, a very few fatigue–life experiments are carried out in the high‐cycle domain to determine the intercept of the structure's S–N curve. By considering the scatter from the material's P–S–N curve, different SSALT designs for the structural component can be composed and checked for their expected acceleration factor. The procedure is experimentally validated for the case of a notched specimen and two different SSALT designs. From the results it can be concluded that the predicted durations of the SSALT experiments correlate well with the real experiments. [ABSTRACT FROM AUTHOR]

A Ti-18Zr-15Nb (at%) shape memory alloy was subjected to a high-temperature thermomechanical treatment (HTMT) combining an equal channel angular pressing (ECAP) at 500 °C for n = 4–8 passes and a short-time post-deformation annealing (PDA) at 600 °C. The phase composition, microstructure, texture, mechanical and functional properties were studied. The functional fatigue behavior observed in this study was compared to that resulted from the reference low-temperature thermomechanical treatment (LTMT) by ECAP at 200 °C for 3 passes + PDA (600 °C for 5 min). The ECAP at 500 °C (n = 4) led to the formation of a highly deformed, dynamically polygonised substructure of β -phase with a crystallographic texture close to the [101] direction. In this state, the alloy exhibited an excellent combination of the static functional and mechanical properties: a relatively high strength (UTS = 670 MPa), a sufficient ductility (δ = 13.3 %), a low Young's modulus (E < 40 GPa), and a high superelastic recovery strain (ε r se max = 3. 1 %). An increase in the number of passes during ECAP to n = 8 led to a greater substructural hardening of the material, grain/subgrain refinement, and the release of α -phase. This significantly increased the alloy strength (UTS = 897 MPa), but reduced its ductility (δ = 5.9 %) and suppressed martensitic transformation. The alloy after both the HTMT (ECAP at 500 °C, n = 4) and TMT (ECAP at 200 °C, n = 3) processes exhibited an equally excellent functional fatigue resistance accompanied by a superior superelastic behavior with small accumulated strains. However, the HTMT process appears to be more technologically advanced, as it eliminates the need for PDA and reduces the risks of specimen cracking during processing. • Ti-Zr-Nb shape memory alloy was subjected to high temperature ECAP. • Dynamically polygonized submicro subgrain structure was formed. • Alloy exhibits an excellent combination of strength and superelastic properties. • Superior functional fatigue behavior after different ECAP regimes. [ABSTRACT FROM AUTHOR]

The positive combination of lightweight design and high fatigue resistance of fiber reinforced materials has led to their broad application in many different structural applications. During the design phase, it is often only considered that these materials are subjected to tensile loading conditions to make use of their excellent strength and fatigue resistance properties. However, in the current challenge to reduce weight of transportation vehicles, a broadening range of loading conditions for composites may arise, whereby it is not always possible to restrict loading to pure tensile conditions. In contrast to metals, compressive loading is a challenging load case for composites. Much research is undertaken to understand the compressive behavior of composites and to develop valid methods for their characterization. Especially for compressive fatigue testing (load ratio R < 0 and R > 1), the generally accepted methods are rare, and not much is reported in the literature on how characterization should be done. This review provides an overview of existing methods, i.e., setups for testing fiber reinforced polymer composites under compression and discusses their applicability to fatigue testing. [ABSTRACT FROM AUTHOR]

Background: Rapid onset of muscular fatigue is still one of the main issues of functional electrical stimulation (FES). A promising technique, known as distributed stimulation, aims to activate sub-units of a muscle at a lower stimulation frequency to increase fatigue-resistance. Besides a general agreement on the beneficial effects, the great heterogeneity of evaluation techniques, raises the demand for a standardized method to better reflect the requirements of a practical application.Methods: This study investigated the fatigue-development of 6 paralysed quadriceps muscles over the course of 180 dynamic contractions, evaluating different electrode-configurations (conventional and distributed stimulation). For a standardized comparison, fatigue-testing was performed at 40% of the peak-torque during a maximal evoked contraction (MEC). Further, we assessed the isometric torque for each electrode-configuration at different knee-extension-angles (70°-170°, 10° steps).Results: Our results showed no significant difference in the fatigue-index for any of the tested electrode-configurations, compared to conventional-stimulation. We conjecture that the positive effects of distributed stimulation become less pronounced at higher stimulation amplitudes. The isometric torque produced at different knee-extension angles was similar for most electrode-configurations. Maximal torque-production was found at 130°-140° knee-extension-angle, which correlates with the maximal knee-flexion-angles during running.Conclusion: In most practical applications, FES is intended to initiate dynamic movements. Therefore, it is crucial to assess fatigue-resistance by using dynamic contractions. Reporting the relationship between produced torque and knee-extension-angle can help to observe the stability of a chosen electrode-configuration for a targeted range-of-motion. Additionally, we suggest to perform fatigue testing at higher forces (e.g. 40% of the maximal evoked torque) in pre-trained subjects with SCI to better reflect the practical demands of FES-applications. [ABSTRACT FROM AUTHOR]

Fatigue testing in kingpins consists in applying cyclic forces to simulate the mechanical loads experienced by this automotive component in practice. In this context, Laboratório de Metalurgia Física (LAMEF) has a quality system implemented as suggested by ISO/IEC 17025 standard, and for the test to be under the management structure, the method must be validated. Method validation is a documented evidence that represents the standardization and indicates its suitability for a certain purpose. Therefore, this work presents the method validation for fatigue tests in kingpins. Thus, selectivity, linearity, sensitivity, range, precision, accuracy, stability and robustness were used as validation criteria. The interpretation of each criterion showed a suitable performance and guaranteed the method validation according the methodology proposed. [ABSTRACT FROM AUTHOR]

In order for additive manufacturing to become a viable manufacturing method for aerospace engineering, it is required that exhaustive static and fatigue testing be performed. The testing is required in order to describe material properties in a statistical manner. Fatigue tests were performed on standard additive manufactured ASTM E466 test specimens in order to obtain the low (1000 cycles) to high cycle (1E6 cycles) behaviour of AlSi10Mg. The specimens were manufactured using non-heat treated, but stress relieved specimens. Specimens were printed in three build directions, namely the XY (parallel with build plate), 45 degree and vertical direction as measured with respect to the build baseplate. The three different directions were chosen to investigate the sensitivity of the material properties to the build direction. The specimens were stress relieved on the baseplate. Static testing was also performed on specimens according to ASTM E8/E8M. The specimens were produced to have a surface finish representative of standard deburring techniques used in the aerospace industry. The surface roughness on the specimens were measured. The scatter in test data as a result of the surface finish on material properties is quantified. It is a requirement to quantify the effect of the surface roughness on fatigue failure allowable values since a machined type finish (less than 3.2 micrometer) is not always practically possible to achieve with additive manufactured structures. This is because the organic shapes produced with additive manufacturing makes some surfaces inaccessible to normal surface finishing techniques. Furthermore, some internal structures such as lattice structures are completely inaccessible to surface finishing techniques such as polishing or lapping. In addition to the surface roughness the roundness of the test section was also measured using inspection equipment. This was required since the industrial deburring techniques did not yield a completely concentric test section as a lathe operation would produce. Once again this is representative of an additive manufactured structure. The fatigue tests were performed at an R-ratio of 0.1. The test results were used to produce Wöhler or S-N curves for the material in all three material directions. The scatter was quantified using industry accepted methods. The results were compared with fatigue test results from literature of specimens produced with a lathe in order to compare a practical industrial surface finish on an additive manufactured component with a machined surface finish. It was found that the build support structures of the additive manufacturing process causes stress concentrations in the fatigue test specimens. This leads to a reduction in fatigue life and an increase in the scatter of the results. [ABSTRACT FROM AUTHOR]

This study describes an approach to quantify the effect of the bending moment on the fatigue strength of a bolt in bolt/nut assembly. To confirm the validity of the conventional fatigue design methodology based on the nominal stress acting on the specified nominal stress area, both the fatigue tests with various bending stress ratios (nominal bending stress/ nominal total axial stress) and the 3D-FE stress analysis for the corresponding conditions were conducted. The results from fatigue tests using a newly developed fatigue testing fixture clearly show as bending stress ratio increases, the (virtual) fatigue strength expressed by the nominal stress also increases. The results from 3D-FE analysis show that the magnitude of the local bending stress on the thread root is lower than the one estimated from nominal axial stress and the stress concentration factor for purely tensile loading. The results, however, also show that the magnitude of the local stress acting on the bolt thread root is affected by the angular position of nut against the loading axis due to the existence of the incomplete thread of nut at the bearing face side. Finally, it is concluded that the conventional fatigue design methodology is practically acceptable for tensile force combined with bending moment loading, albeit with results that are slightly conservative.

Purpose: The purpose of this study was to determine the fatigue and fracture strength of zirconia implant abutments connected to titanium cores (ZrTi) and one-piece zirconia implant abutments (Zr). Materials and Methods: Thirty-two implants were secured into epoxy resin blocks and connected with abutments. Eight specimens of each group (Zr with a diameter of 3.75 mm [Zr3.75] or 5.5 mm [Zr5.5] and ZrTi with a diameter of 3.75 mm [ZrTi3.75] or 5.5 mm [ZrTi5.5]) were thermally cycled from 5°C to 55°C and loaded with 100,000 cycles at 120 N at 30 degrees off-axis. All specimens were then tested for fracture resistance using a compressive load at 30 degrees off-axis. Results: Abutment fracture or screw loosening was not observed during thermal cycling and cyclic loading. The median fracture resistance values and standard deviations were 526 N (± 32 N) for group Zr3.75, 1,241 N (± 269 N) for group ZrTi3.75, 1,894 N (± 137 N) for group Zr5.5, and 2,225 N (± 63 N) for group ZrTi5.5. Statistically significant differences in fracture strength were found between Zr and ZrTi for each implant diameter. Conclusions: Zirconia implant abutments connected to titanium cores showed higher fracture strength compared to one-piece zirconia abutments. Hence, they might be preferable for clinical use. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to evaluate the role of the implant/abutment system on torque maintenance of titanium retention screws and the vertical misfit of screw-retained implant-supported crowns before and after mechanical cycling. Materials and Methods: Three groups were studied: morse taper implants with conical abutments (MTC group), external-hexagon implants with conical abutments (EHC group), and external-hexagon implants with UCLA abutments (EHU group). Metallic crowns casted in cobalt-chromium alloy were used (n = 10). Retention screws received insertion torque and, after 3 minutes, initial detorque was measured. Crowns were retightened and submitted to cyclic loading testing under oblique loading (30 degrees) of 130 ± 10 N at 2 Hz of frequency, totaling 1 × 106 cycles. After cycling, final detorque was measured. Vertical misfit was measured using a stereomicroscope. Data were analyzed by analysis of variance, Tukey test, and Pearson correlation test (P < .05). Results: All detorque values were lower than the insertion torque both before and after mechanical cycling. No statistically significant difference was observed among groups before mechanical cycling. After mechanical cycling, a statistically significantly lower loss of detorque was verified in the MTC group in comparison to the EHC group. Significantly lower vertical misfit values were noted after mechanical cycling but there was no difference among groups. There was no significant correlation between detorque values and vertical misfit. Conclusions: All groups presented a significant decrease of torque before and after mechanical cycling. The morse taper connection promoted the highest torque maintenance. Mechanical cycling reduced the vertical misfit of all groups, although no significant correlation between vertical misfit and torque loss was found. [ABSTRACT FROM AUTHOR]

In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing, the influence of gravity on the performance of excitation equipment and fatigue damage evaluation of the different positions of wind turbine blades are analyzed. With the multi-excitation loading in the horizontal direction, the actuator force of the excitation equipment does not need to overcome the gravity of the dynamic mass, w'hich directly outputs the exciting force of the system vibration. The excitation efficiency of the equipment is 77% higher than that of the vertical load. The gravity moment of the horizontal loading mode is perpendicular to the loading direction. That is, the mean load in the flapwise direction is zero. The weight of excitation equipment could replace the tuning mass on the condition that the self-weight of equipment is reduced by the multi-excitation mode, which helps the excitation equipment play the comprehensive function of excitation equipment and tuning mass. At the same time, the gravity moment in the edgewise direction will be decreased by 17.0%-22.5% under the multi-excitation horizontal loading mode. In the vertical loading mode, the gravity moment is the mean load, which only increases fatigue damage accumulation by 15.6%. By comparing the role of gravity in the excitation equipment and fatigue damage evaluation, the multi-excitation horizontal loading mode has more advantage to performance the exciting force than the contribution of gravity to the fatigue damage accumulation in the vertical loading mode. Through the fatigue testing of multi-excitation horizontal loading, the potential of excitation equipment is explored, and the problem of insufficient exciting force in large fullscale wind turbine blade fatigue testing will be solved. [ABSTRACT FROM AUTHOR]

The fatigue behaviour of a biaxial carbon/epoxy Non-Crimp-Fabric (NCF) composite is evaluated at room temperature and 130o C for automotive applications. A new specimen geometry is developed allowing three stress ratios R = 0.1, R = −1 and R = 10 to be tested at 130o C without the use of anti-buckling fixtures for axial loadings. The three stress ratios show good agreement in fatigue life using an equivalent stress amplitude. The fracture surfaces from failed fatigue test specimens are compared to those of monotonic loading to evaluate the changes to failure modes under the different loading conditions. Tensile dominated loading such as uniaxial tension and fatigue testing with R = 0.1 result in delamination of the NCF material coupled with fibre failure along the loading direction as the primary failure modes. Compressive fatigue failures at 130 °C occur at an inclined angle through thickness due to a shearing process along with fibre kinking. The matrix material exhibits more ductile characteristics at 130o C altering the fracture surfaces at elevated temperature. [ABSTRACT FROM AUTHOR]

This paper proposes an alternating bending technique for evaluating fatigue life in the low‐to‐high cycle fatigue regime. A method was developed for estimating the stress, elastic strain, and plastic strain ranges of a plastically deformed specimen subjected to alternating bending with consideration of stress and strain distributions. To evaluate its effectiveness, fatigue testing was conducted using a specimen made of a steel used for pressure vessels. The stress, elastic strain, and plastic strain ranges could be obtained during cyclic bending. The elastic strain amplitude life and plastic strain amplitude life curves were linear in a log–log plot in the low‐to‐high cycle fatigue regime. Hence, the fatigue life under alternating bending could be evaluated using the proposed strain‐based approach. However, these curves could not be predicted using equations with parameters obtained from tensile testing, such as the universal slope method, due to the strain gradient in the specimen. [ABSTRACT FROM AUTHOR]

Hot‐work tool steels are exposed to complex interacting cyclic thermal and mechanical loadings. Due to the combination of strengthening via carbides and intermetallic precipitates, dual hardening steels achieve well‐balanced mechanical properties in terms of fatigue strength and fracture toughness. Therefore, dual hardening steels have a great potential for hot‐work applications. Herein, out‐of‐phase thermomechanical fatigue tests are used to simulate the loading conditions experienced in hot‐work tool steel applications on a laboratory scale. The testing is conducted on Fe–C–Cr–Mo–V and Fe–C–Cr–Mo–V–Ni–Al alloys to compare common 5% Cr and dual hardening hot‐work tool steels. The resistance to thermomechanical fatigue is therefore correlated with single or dual hardening. Both alloys experience softening during the fatigue testing. Atom probe tomography investigations reveal coarsening of the secondary hardening precipitates for both alloys. However, the number density of surface cracks is greater for the 5% Cr hot‐work tool steel. The dual hardening steel possesses higher resistance to softening and reaches a higher lifetime. [ABSTRACT FROM AUTHOR]

Accidents occurring on railway track of 1520 nun are often associated with the fracture of cast load-carrying elements of three-element freight car trucks. The level of quality and endurance of such truck elements as side frame and truck bolster, which are traditionally manufactured by casting technology, are insufficient, so it is advisable to use welding technology to manufacture the mentioned parts of sheet rolled metal in order to increase the fatigue resistance characteristics. The development of a new all-welded structure of side frame of a three-element freight car truck with an axial load of 23.5 tc was carried out on the basis of widespread use of mathematical modelling to determine the stress-strain state of welded elements of the truck under the action of a regulated range of loads and to evaluate the strength according to the valid standards and modem global approaches. The technology of assembly and welding, as well as the appropriate specialized equipment for manufacture of a developed design of welded side frame were created. Two test specimens were manufactured and accelerated fatigue tests were carried out. the results of which showed a significant increase in endurance and vitality under operational cyclic loads as compared to designs of existing cast side frames. Taking into account high values of reliability, availability and manufacturability, ability of a significant reduction in unsprung weight and increase in dimensional accuracy, the welded structure of the side frame of a three-element freight car truck is very promising for its implementation on railway track of 1520 mm. [ABSTRACT FROM AUTHOR]

The accidents occurring on railway track of 1520 mm are often associated with the fracture of cast load-carrying elements of three-element freight car bogies. The level of quality and endurance of such bogie elements as side frame and bogie bolster, which are traditionally manufactured by casting technology, are insufficient, so it is advisable to use welding technology to manufacture the mentioned parts of sheet rolled metal in order to increase the fatigue resistance characteristics. The development of a new all-welded structure of side frame of a three-element freight car bogie with an axial load of 23.5 ts was carried out on the basis of widespread use of mathematical modelling to determine the stress-strain state of welded elements of the bogie under the action of a regulated range of loads and to evaluate the strength according to the valid standards and modem global approaches. The technology of assembly and welding, as well as the appropriate specialized equipment for manufacture of a developed design of welded side frame were created. Two test specimens were manufactured and accelerated fatigue tests were carried out, the results of which showed a significant increase in endurance and vitality under operational cyclic loads as compared to designs of existing cast side frames. Taking into account high values of reliability, availability and manufacturability, ability of a significant reduction in unsprung weight and increase in dimensional accuracy, the welded structure of the side frame of a three-element freight car bogie is very promising for its implementation on railway track of 1520 mm. [ABSTRACT FROM AUTHOR]

Ships and offshore structures may be operated in areas with seasonal freezing temperatures and extreme environmental conditions. While current standards state that attention should be given to the validity of fatigue design curves at subzero temperatures, studies on fatigue strength of structural steel at subzero temperatures are scarce. This study addresses the issue by analysing the fatigue strength of welded steel joints under subzero temperatures. Although critical weld details in large welded structures are mostly fillet‐welded joints, most published data are based on fatigue crack growth rate specimens cut out of butt‐welded joints. This study analyses fillet‐welded specimens at −20°C and −50°C against controls at room temperature. Significantly higher fatigue strength was measured in comparison to estimates based on international standards and data from design codes even at temperatures far below the allowed service temperature based on fracture toughness results. [ABSTRACT FROM AUTHOR]

Continuous casting leads to the formation of voids, which can be considered as an initial state of damage. During hot rolling these voids shall be closed, reducing this initial damage and avoiding its negative influence on the mechanical properties and performance of the produced material. However, hot rolling also influences the microstructure, which in turn affects the performance e.g. the fatigue strength. So far, little research has been published on the separation of those influencing factors. This paper is a first attempt to separate the influence of damage from the microstructure in hot rolling. Numerical simulation is utilized to study void closure throughout the multi-pass process while the evolution of microstructure and damage is investigated experimentally using numerous characterization methods. Two process routes with a large and a small pass reduction have been investigated and comparable microstructures have been achieved. A continuous damage reduction throughout the rolling process has been observed by means of void distribution and density measurements. The large pass reduction showed a slightly reduced damage and an increased fatigue strength in all considered thicknesses, however this could not be traced back to the damage reduction exclusively. [ABSTRACT FROM AUTHOR]

Asphalt self-healing with encapsulated rejuvenators is a new promising approach to extend the service life of asphalt pavements. Although the research performed so far has demonstrated the crack healing mechanism, no formulation/design for the capsule-bituminous mixture system, aiming to optimize its performance properties, has yet been proposed. This study investigates the effect of calcium-alginate capsules, containing sunflower oil, on the mechanical properties of bituminous mixtures. Performance-related properties of a continuously-graded bituminous mixture (stiffness, fatigue and rutting) were evaluated for different dosages of capsule incorporation (0.50, 0.75 and 1.00 wt%). The results showed that the stiffness properties of the bituminous mixture are affected by capsules and that this effect evolves with bitumen ageing. The stiffness modulus after ageing treatment was close to the bituminous mixture with 0.50 wt% and 0.75 wt% capsules and to the reference material. The fatigue resistance of all bituminous mixtures was similar and the bituminous mixtures with capsules did not show an improvement in fatigue resistance after resting, in comparison with the reference material. However, the results clearly indicated that the rejuvenator was released from the capsules and diffused into the bitumen. The bituminous specimens with capsules showed a strong rutting resistance, and the performance was even improved after the rest period. [ABSTRACT FROM AUTHOR]

The concept of cold-bent shallow press-brake-formed steel tub girders was developed by a technical working group within the Steel Market Development Institute's (a business unit of the American Iron and Steel Institute) Short Span Steel Bridge Alliance, led by the current authors. This working group consists of all stakeholders in the steel bridge industry, including mills, fabricators, service centers, industry trade organizations, universities, and bridge owners. The scope of this effort is defined by three separate tasks. First, singular composite girders were fatigue tested by simulating a 75-year life in a rural environment. Second, two slab edge treatment methods were evaluated to determine the optimal option for the Ultra-High Performance Concrete (UHPC) joint between modular tub girder units. Lastly, two composite modular press-brake-formed tub girders were connected longitudinally with a UHPC joint and the system's fatigue performance was evaluated. Experimental results show press-brake-formed tub girders behave adequately with respect to fatigue. Longitudinal joints composed of UHPC behaved satisfactorily throughout testing. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to use a clinical simulation to determine whether wear of the internal surface of a titanium implant was greater following connection and loading of a one-piece zirconia implant abutment or a titanium implant abutment. Materials and Methods: Two implants received zirconia abutments and two received titanium abutments. The implants were secured into four fiber-reinforced epoxy resin disks that had been prepared to receive the internal-connection implants. The assemblies were cyclically loaded off-axis for a total of 1,000,000 cycles. At various intervals, the abutments were removed, photographed, examined using scanning electron microscopy (SEM), and returned to the implants for further testing. The area of titanium transfer from the implants to the abutments observed in the SEM images was quantified using image analysis software. Results: The method was able to quantify the area of material transferred to the abutments. There was considerably more wear associated with the zirconia abutments, but the rate of wear slowed after about 250,000 cycles. Parabolic curves were fit to the data. The projected mean ± standard deviation maximum area (wear) values associated with the titanium and zirconia abutments were 15.8 ± 3.3 × 103 μm2 and 131.8 ± 14.5 × 103 μm2, respectively, and this difference was statistically significant (P = .0081). Conclusions: The implants with the zirconia abutments showed a greater initial rate of wear and more total wear than the implants with the titanium abutments following cyclic loading. The amount of titanium transfer seen on the zirconia abutment increased with the number of loading cycles but appeared to be self-limiting. The clinical ramifications of this finding are unknown at this time; however, the potential for component loosening and subsequent fracture and/or the release of particulate titanium debris may be of concern. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments used in ZirDesign (Astra Tech) implant/tooth-supported fixed partial dentures (FPDs) in the maxilla. Materials and Methods: Four different test groups (n = 8) representing anterior implant/tooth-supported FPDs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (maxillary left central incisor) from a prosthetic point of view, which allowed for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position that required an angulated (20-degree) abutment. OsseoSpeed implants (4.5 × 13 mm, Astra Tech) as well as metal tooth analogs (maxillary right lateral incisor) with simulated periodontal mobility were mounted in polymethyl methacrylate. The FPDs (chromium-cobalt alloy) were cemented with glass ionomer. Groups 2 and 4 were thermomechanically loaded and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. Results: All samples survived thermomechanical loading. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the straight abutments or the angulated abutments. The restorations that used angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1: 209.13 ± 39.11 N; group 2: 233.63 ± 30.68 N; group 3: 324.62 ± 108.07 N; group 4: 361.75 ± 73.82 N). This difference in loadbearing performance was statistically significant, both with and without artificial aging. All abutment fractures occurred below the implant shoulder. Conclusions: Compensation for angulated implant positions with an angulated zirconia abutment is possible without reducing the load-bearing capacity of implant/tooth-supported anterior [ABSTRACT FROM AUTHOR]

This work presents a new resonance-based testing facility for axially loaded structural elements for performing efficient fatigue tests. Two different configurations make it possible to test specimens either under compressive or under tensile loads. In both cases, a mean load is applied. In contrast to conventionally used servo-hydraulic actuators, synchronised imbalance motors with low energy input were used, which allow to generate cyclic loads with high loading frequencies. By setting the excitation frequencies of the motors close to the natural frequency of the system resonant behaviour occurs, which results in a dynamic amplification. Thus, input forces and test duration can be reduced. As a verification of the developed testing facility, two tests, one in each configuration, were carried out and analysed. • A resonance-based testing facility with imbalance motors was developed. • Structures can be tested axially in compression and tension. • A flexible mean load can be applied. • The function and applicability of the testing facility was proven by two exemplary fatigue tests. [ABSTRACT FROM AUTHOR]

• Bio-oil derived from biodiesel production induces the binder softening. • Fatigue resistance is improved with the bio-oil incorporation. • Healing follows an exponential law with the duration of the rest period. • Different healing indexes provide different results. • Healing index is mostly influenced by the complex shear modulus. Road pavements are exposed to traffic and temperature effects that produce distress, mainly cracking that leads to pavement failure, after which rehabilitation actions are necessary to extend pavement life. Bio-rejuvenators have been used to recover the bitumen properties lost due to fatigue of the asphalt mixtures and ageing due to temperature variations and oxidation. Thus, this paper investigates the healing of bitumen modified with bio-oil derived from biodiesel production. One base bitumen in three different ageing stages (unaged, short and long-term ageing) was used for adding up to 3% of bio-oil to the bitumen. In addition to consistency and rheological tests to characterise the modified bitumen, fatigue resistance tests with and without rest periods were performed to assess the healing through three indexes, relating the complex shear modulus, the number of cycles to failure and the amount of damage, after a rest period. It was verified that the healing follows an exponential law with the rest period, but the number of cycles in each loading period decreases compared to the previous period. For a 15-minute rest period, the healing was limited to 26.9%, but the bio-oil contributed significantly to that restoration. [ABSTRACT FROM AUTHOR]

Additively manufactured (AM) metallic components are known to contain distributed geometric discontinuities both internally and at surface. Their effects on fatigue behaviors of AM parts or components need to be better understood for developing cost-effective AM process qualification and part performance certification procedures for safety-critical applications. In this investigation, a rapid fracture mechanic modeling technique is adopted for evaluating the interactions of multiple crack-like defects and their effects on fatigue behaviors of AM test specimens. The parametric study is performed by varying the spacing between defects and the orientations of the defects with respect to the loading direction as well as their proximity to unnotched and notched test specimens. Then, the interactions of defects are examined, and the criterion for treating multiple cracks as a single equivalent crack is presented and compared with existing interaction criteria, e.g., those by ASME XI and BS 7910. Based on the findings of this study, a proposed approach for treating multiple crack-like defects, particularly in highly stressed regions, e.g., near a notch location is presented. Available fatigue test data from unnotched and notched AM specimens have also been analyzed to validate the proposed approach. • Model defect interactions in unnotched and notched additively manufactured specimens. • Develop a robust, reliable and rapid multi-crack stress intensity factor method. • Present a defect interaction diagram with consideration of amplification and shielding effects. • Develop a fast quantitative statistical method for defect size and spacing evaluation. • Present fatigue test data correlation with different AM alloys, specimens, types and etc. [ABSTRACT FROM AUTHOR]