Millions Of Cycles Research Articles

An adaptive acceleration scheme for phase-field fatigue computations

Abstract Phase-field models of fatigue are capable of reproducing the main phenomenology of fatigue behavior. However, phase-field computations in the high-cycle fatigue regime are prohibitively expensive due to the need to resolve spatially the small length scale inherent to phase-field models and temporally the loading history for several millions of cycles. As a remedy, we propose a fully adaptive acceleration scheme based on the cycle jump technique, where the cycle-by-cycle resolution of an appropriately determined number of cycles is skipped while predicting the local system evolution during the jump. The novelty of our approach is a cycle-jump criterion to determine the appropriate cycle-jump size based on a target increment of a global variable which monitors the advancement of fatigue. We propose the definition and meaning of this variable for three general stages of the fatigue life. In comparison to existing acceleration techniques, our approach needs no parameters and bounds for the cycle-jump size, and it works independently of the material, specimen or loading conditions. Since one of the monitoring variables is the fatigue crack length, we introduce an accurate, flexible and efficient method for its computation, which overcomes the issues of conventional crack tip tracking algorithms and enables the consideration of several cracks evolving at the same time. The performance of the proposed acceleration scheme is demonstrated with representative numerical examples, which show a speedup reaching up to four orders of magnitude in the high-cycle fatigue regime with consistently high accuracy. Graphical abstract

Soil mechanics principles for modelling railway track performance

Predicting the performance of railway track is difficult owing to the complex and repeated nature of the loading, the many millions of cycles applied over the life of the structure, the need to characterise the often-infinitesimal rate of accumulation of plastic settlement, and the importance of differential settlements in the along-track direction, which can adversely impact train ride and passenger comfort. These come in addition to the usual soil mechanics challenges of reproducing in a constitutive model the real behaviour of soil and soil-like materials such as railway ballast. Degradation of the geomaterials comprising the trackbed and the underlying ground or earthwork owing to mechanical and environmental effects is a further concern. The paper discusses these issues and explores the application of fundamental soil mechanics principles and advanced constitutive models to understanding and quantifying their effects on railway track and trackbed performance. Recommendations for future research are made.

Nondissipative Martensitic Phase Transformation after Multimillion Superelastic Cycles.

Superelastic alloys used for stents, biomedical implants, and solid-state cooling devices rely on their reversible stress-induced martensitic transformations. These applications require the alloy to sustain high deformability over millions of cycles without failure. Here, we report an alloy capable of enduring 10×10^{7} tensile stress-induced phase transformations while still exhibiting over 2% recoverable elastic strains. After millions of cycles, the alloy is highly reversible with zero stress hysteresis. We show that the major martensite variant is reversible even after multimillions of cycles under tensile loadings with a highly coherent (11[over ¯]0)_{A} interface. This discovery provides new insights into martensitic transformation, and may guide the development of superelastic alloys for multimillion cycling applications.

Power Cycling on Lateral GaN and β-Ga<sub>2</sub>O<sub>3</sub> Transistors

The load cycling capability of novel power semiconductors is an important aspect when estimating their lifetime in field service. The Power Cycling Test (PCT) is the standard test to evaluate the lifetime of a semiconductor device under thermo-mechanical stress. PCTs are typically performed at temperature swings (ΔT) much higher than common operating conditions, to obtain results within a reasonable time. In this work, the PCT capability of gallium nitride (GaN) and gallium oxide (Ga2O3) lateral transistors is investigated. The GaN devices were tested in two groups with different ΔT. The temperature of the devices was monitored using two different temperature sensitive electrical parameters (TSEPs) and the accuracy of both methods was evaluated by comparing the results with the temperature, monitored by using an infrared (IR) camera. For Ga2O3 devices, no data on potential TSEP exists so far, thus, the typical TSEP for silicon (Si), silicon carbide (SiC) and GaN were investigated for their applicability to Ga2O3 devices. While a PCT was conducted on the devices, the temperature was also monitored using an IR camera. The results of the comparison of TSEP and IR camera data showed, that the accuracy of the TSEP for GaN matched either the temperature of the hottest spot on the chip (VDS method), or the average chip temperature (VGS method). For the Ga2O3 devices no suitable TSEP could be obtained and only the IR camera was used for the temperature measurement. It revealed a very uneven temperature and thus, current distribution on the chip. Furthermore, both GaN and Ga2O3 devices exhibit an outstanding power cycling capability with no failure after completing several millions of cycles. Considering the difference in Young’s Modulus of Si, GaN and Ga2O3, the PCT performance of GaN on silicon devices and Ga2O3 devices should be inferior to silicon devices. Thus, both device types, the GaN transistors and the Ga2O3 transistors, showed a PCT capability much higher than expected.

On-demand heart valve manufacturing using focused rotary jet spinning

On-demand heart valve manufacturing using focused rotary jet spinning

P-y based approach to predicting the response of monopile embedded in soft clay under long-term cyclic loading

Offshore wind turbines (OWTs) are subjected to environmental loadings such as those induced by waves or wind typically comprising up to millions of cycles (i.e., high-cycle loading). To evaluate the performance of OWTs during a lifetime cycle, this study proposed a p-y based approach to predict monopile response subjected to a long-term cyclic loading. A cyclic loading may cause an accumulation of strain and a built-up of excess pore water pressure under undrained conditions, accompanied by a corresponding reduction of stiffness and shear strength in soft marine clay. In the proposed procedure, the cyclic degradation and strain accumulation of soft clay is considered by a generalized empirical model given the soil reaction calculated from p-y analysis for a prescribed loading condition on the pile. Afterward, the response of pile subjected to a long-term cyclic loading is predicted by modifying the preselected p-y curve by p-multiplier and y-multiplier to take account for the cyclic degradation and strain accumulation, respectively. The proposed approach is validated by three centrifuge tests on a monopile in soft clay. The simulation results are in good accordance with the measurements in terms of pile displacement and bending moment versus number of applied cycles. Therefore, the proposed approach is feasible to predict the long-term pile response subjected to high-cycle loading. Moreover, it is easily implemented in the widely used p-y approach.

A tractable mathematical model for rectified diffusion

A core unresolved challenge in rectified diffusion is the lack of predictive models, which allow accurate modelling of the growth of bubbles over millions of cycles of oscillation. The spherically symmetric problem involves two asymptotic regions in space for the convection and diffusion of the dissolved gas in the liquid, an inner region adjacent to the bubble and an outer region. It also involves three time scales: the shortest time scale associated with the bubble oscillation, the intermediate and the longest time scales for the mass transport across the bubble interface and the outer region, respectively. The problem is analysed systematically using matched asymptotic expansions in space and multi-scales in time, the large parameter being the Péclet number for mass transfer. A tractable mathematical model is formulated for rectified diffusion. It comprises the Rayleigh–Plesset equation for the spherical oscillations of the bubble on the shortest time scale, an ordinary differential equation for the mass of gas in the bubble on the intermediate time scale and a diffusion equation on the longest time scale and the long length scale. Predictions of this simplified model have excellent agreement with experimental results for a single spherical bubble in the bulk over millions of cycles of oscillation. A parametric study is undertaken with several new phenomena/features observed for acoustic frequencies in the range 12 to 62 kHz, acoustic field $0.12$ to $0.22$ bar and the initial gas concentration in the liquid being $0.95$ to $1.0$ of the saturation concentration.

Three-dimensional mapping of mineral in intact shark centra with energy dispersive x-ray diffraction

The centra of shark vertebrae consist of cartilage mineralized by a bioapatite similar to bone's carbonated hydroxyapatite, and, without a repair mechanism analogous to remodeling in bone, these structures still survive millions of cycles of high-strain loading. The main structures of the centrum are an hourglass-shaped double cone and the intermedialia which supports the cones. Little is known about the nanostructure of shark centra, specifically the relationship between bioapatite and cartilage fibers, and this study uses energy dispersive diffraction (EDD) with polychromatic synchrotron x-radiation to study the spatial organization of the mineral phase and its crystallographic texture. The unique energy-sensitive detector array at beamline 6-BM-B, the Advanced Photon Source, enables EDD to quantify the texture within each sampling volume with one exposure while constructing 3D maps via specimen translation across the sampling volume. This study maps a centrum from two shark orders, a carcharhiniform and a lamniform, with different intermedialia structures. In the blue shark (Prionace glauca, Carcharhiniformes), the bioapatite's c-axes are oriented laterally within the centrum's cone walls but axially within the wide wedges of the intermedialia; the former is interpreted to resist lateral deformation, the latter to support axial loads. In the shortfin mako (Isurus oxyrinchus, Lamniformes), there is some tendency for c-axis variation with position, but the situation is unclear because one dimension of the sampling volume is considerably larger than the thickness and spacing of the intermedialia's radially-oriented lamellae. Because elastic modulus in collagen plus bioapatite mineralized tissues varies significantly with both volume fraction of bioapatite and crystallographic texture, the present 3D EDD-derived maps should inform future 3D numerical models of shark centra under applied load.

A new finite element procedure for simulation of flexural fatigue behaviours of hybrid engineered cementitious composite beams

This study proposes a new finite element (FE) analysis procedure for simulation of flexural fatigue behaviours of hybrid fibre reinforced engineered cementitious composite (hybrid ECC) beams. The proposed method simplifies the analysis of hybrid ECC beams under fatigue loading, which could have fatigue life up to millions of cycles, into a small number of static FE analyses corresponding to a set of designated load cycles with equivalent fatigue damages. An ECC material damage model is first developed to describe the degrading of material properties caused by fatigue loading. This material damage model defines the relationships of two critical damage properties of ECC, namely the degraded stiffness and the accumulated plastic strain with the number of load cycles applied. By using the developed material damage model, a simplified analysis procedure is then proposed for the fatigue analysis of hybrid ECC beams under bending. The accuracy and reliability of the proposed material damage model and analysis procedure are validated by comparing experimental results obtained from bending tests of three types of hybrid ECC beams under three different stress ranges with the modelling predictions. It is found that the proposed material damage model and analysis procedure provided good predictions of the fatigue responses of the hybrid ECC beams in terms of material damages, deformation and fatigue life.

Very high cycle fatigue behaviour of S690 structural steel

Testing beyond 10 millions of cycles in a conventional fatigue machine is a very time consuming task, so the fatigue limit has been settled around this number of cycles. However, during the service life, several engineering components experience a number of cycles larger than 10 million cycles. For that reason, the region of very high cycle fatigue (VHCF), and the concept of fatigue limit has been matter of study and interest in the last decades. In order to overcome the time effort required, ultrasonic fatigue testing machine has being developed and widely used. Nevertheless, ultrasonic testing system and the VHCF region brought new challenges such as the frequency effect and the internal crack initiation. Thus, this research work intends to characterize the fatigue behaviour of S690 structural steel in the VHCF region. An experimental campaign of twenty specimens was performed in ultrasonic testing machine at a frequency of 20 kHz and a mean curve was determined. This work also approaches a design methodology of smooth fatigue specimens to be tested in ultrasonic fatigue machine.

Development of a Vibration Technique Based on Geometric Optimization for Fatigue Life Evaluation of Sandwich Composite Structures

A major obstacle to obtaining cost-effective experimental data on the fatigue life of sandwich panels is the prohibitive amount of time and cost required to carry out millions of cycles. On the other hand, vibration techniques applied to sandwich geometries fail to match the stress patterns that are obtained from standard flexural fatigue tests. To overcome such limitations, a vibration-based fatigue technique is proposed, which entails the use of sandwich specimens whose geometries are optimized to reproduce the stress distribution observed during three point bend loading while vibrating at the first resonant frequency. The proposed vibration technique was experimentally validated. The results, compared with the average number of cycles to failure at different stress ratios obtained via the Three-Point Bending test, showed high levels of accuracy. The proposed method is robust and time effective and indicates the possibility of attaining fatigue lifetime prediction of a wide class of composite elements, such as sandwich panels.

Conformable metal oxide platelets – A smart surface armor for green tribology

The reduction of friction and wear is a crucial performance criterion for most technical processes. This is particularly true for the ubiquitous case of oil lubricated machinery made from steel components. Here we introduce a facile laser treatment that significantly enhances the tribological performance of bearing steel 100Cr6, a material widely used for the manufacture of ball and roller bearings. By applying repeated nanosecond-pulses of focussed laser-beam irradiation under ambient air, a surface-protective tribo-layer is generated by a method that exploits self-organization for the formation of conformable metal oxide platelets consisting of vertically aligned transition metal oxides nanorods on the steel substrate. These submicron-sized metal oxide platelets protect the surfaces similar to scale armor and the tribological performance of the bearing steel 100Cr6 was significantly enhanced. Based on laboratory tests using a rotational pin-on-disk tribometer under oil lubricated conditions, close to zero wear with simultaneous reduction of friction by 54% was achieved. Even under the harsh conditions in the pin-on-disk tribometer these metal oxide platelets turn out to be remarkably robust against detachment and crumbling for lasting millions of cycles at a slip rate of 100%. The origin of this resilience is based on a special substructure of the platelets that, counter-intuitively for ceramic material, enables shape adaptations to surface deformations emergent upon high mechanical stress.

Bulk NiTiCuCo shape memory alloys with ultra-high thermal and superelastic cyclic stability

Shape memory alloys sustaining stable functional properties for millions of cycles have been reported in NiTiCuCo thin films. The mechanism behind such ultralow functional fatigue was proposed to originate from the epitaxy strains surrounding coherent Ti2Cu precipitates. Despite having a well-understood microstructural origin, such fatigue-resistant property has never been achieved in bulk NiTiCuCo counterparts. In this study, we first show that the semi-coherent Ti2Cu precipitates help satisfy closely the compatibility criteria under thermal phase transformation. Assisted by aging at 600 °C for 1 h, an unprecedented thermal stability is reported in bulk coarse-grained Ti54Ni31.7Cu12.3Co2, where the transformation temperatures migrate by ∼ 0.1 °C for 200 cycles. To achieve stable superelastic response, a thermomechanical processing route is proposed that results in a uniform nanocrystalline microstructure with embedded Ti2Cu precipitates. Such a microstructure exhibits much improved superelastic cyclic stability as evidenced by ∼ 22 MPa shakedown of plateau stress for 200 superelastic cycles.

The initial run-in and long-term drift of the adhesive force between polycrystalline silicon MEMS sidewalls

In this paper we measure the evolution of adhesion between two polycrystalline silicon sidewalls of a microelectromechanical adhesion sensor during three million contact cycles. We execute a series of AFM-like contact force measurements with comparable force resolution, but using real MEMS multi-asperity sidewall contacts mimicking conditions in real devices. Adhesion forces are measured with a very high sub-nanonewton resolution using a recently developed optical displacement measurement method. Measurements are performed under well-defined, but different, low relative humidity conditions. We found three regimes in the evolution of the adhesion force. (I) Initial run-in with a large of cycle-to-cycle variability, (II) Stability with low variability, and (III) device-dependent long term drift. The results obtained demonstrate that although a short run-in measurement shows stabilization, this is no guarantee for long-term stable behavior. Devices performing similarly in region II, can drift very differently afterwards. The adhesion force drift during millions of cycles is comparable in magnitude to the adhesion force drift during initial run-in. The boundaries of the drifting adhesion forces are reasonably well described by an empirical model based on random walk statistics. This is useful knowledge when designing polycrystalline silicon MEMS with contacting surfaces.

Fatigue Resistance of the Advanta V12/iCast and Viabahn Balloon-Expandable Stent-Graft as Bridging Stents in Experimental Fenestrated Endografting

Purpose: Bridging stents undergo millions of cycles during respiratory movements of the kidneys throughout the patient’s life. Thus, understanding the response of fabric and endoskeleton of the stent to cyclic loading over the time is crucial. In this study, we compare the fatigue resistance of the Viabahn Balloon-Expandable stent-graft (VBX) with the widely used Advanta V12/iCast under prolonged stress induction. Materials and Methods: A polyester test sheet with 10 fenestrations was used simulating a fenestrated endograft. Five 6×59 mm VBX stent-grafts and five 6×58 mm Advanta stent-grafts were implanted into 6×6 mm fenestrations. The stents were flared with a 10×20 mm PTA (percutaneous transluminal angioplasty) catheter and connected with a fatigue stress machine. All stent-grafts were evaluated by microscopy and radiography at baseline and after regular intervals until 50,000,000 cycles were applied, simulating a life span of approximately 75 months. Freedom from fracture (FF), freedom from initial polytertafluoroethylene (PTFE) changes (FIC), and from PTFE breakpoint (FBP, all-layer defect) were calculated. Results: Digital radiographic images did not show any stent fracture in both groups after 50,000,000 cycles. The VBX stent-graft was free from any all-layer defects at the conclusion of 50,000,00 cycles resulting in a significant higher FBP compared with Advanta V12 (50,000,000 vs 33,400,000; p<0.01). All-layer defects were observed only in the Advanta group. Two of 5 Advanta stents showed early penetration of the nitinol ring causing a defect of PTFE. Regarding FIC, there was no significant difference between the stents (3,400,000 in VBX vs 3,200,000 in Advanta). Conclusions: In fatigue tests simulating respiration movements, VBX and Advanta V12 performed equally well in terms of fracture resistance and freedom from initial PTFE changes. VBX maintained freedom from PTFE breakpoint throughout the full 50,000,000 cycles. All-layers defects were detected only in Advanta and were mainly caused by penetration of the nitinol ring through the PTFE.

Fatigue Behavior of 3D Braided Composites Containing an Open-Hole.

The static and dynamic mechanical performances of notched and un-notched 3D braided composites were studied. The effect of longitudinal laid-in yarn was investigated in comparison with low braiding angle composites. The specimens were fatigue tested for up to millions of cycles, and the residual strength of the samples that survived millions of cycles was tested. The cross-section of the 3D braided specimens was observed after fatigue loading. It was found that the static and fatigue properties of low angle 3D braided behaved better than longitudinally reinforced 3D braided composites. For failure behavior, pure braids contain damage better and show less damage area than the braids with longitudinal yarns under fatigue loading. More cracks occurred in the 3D braided specimen with axial yarn cross-section along the longitudinal and transverse direction.

A study of the stress field generated by the contact between a sphere and a flat plate for a simplified model of deep-groove ball bearing

Bearings are mechanical elements capable of transferring motion between two or more parts in a machine. When an external load is applied, the rolling elements and their rings tend to initiate a cyclical movement between themselves. Hence, they are linked by a variable type of contact, thus creating high surface stresses. As these elements are subjected to millions of cycles within their lifespan, these cyclical stresses may create cracks and cause failure by rolling contact fatigue (RCF). Due to the importance of this subject, it is vital to study the stress field caused by contact between the rolling parts in a bearing. This paper offers two approaches on the cyclical stresses in a deep-groove ball bearing: an analytical approach, using Hertz’s theory for contact stresses; and a numerical simulation, using the Finite Element Method (FEM) with the software Inventor and Nastran In-CAD. The results of both approaches were compared, and stress behavior was analyzed as the depth of the inner ring was increased. It was concluded that the surface stresses are greatly superior than the strength of the materials used in the bearings, and that the area influenced by these stresses are small when compared to the dimensions of the whole.

Fatigue-resistant adhesion of hydrogels

The adhesion of soft connective tissues (tendons, ligaments, and cartilages) on bones in many animals can maintain high toughness (∽800 J m−2) over millions of cycles of mechanical loads. Such fatigue-resistant adhesion has not been achieved between synthetic hydrogels and engineering materials, but is highly desirable for diverse applications such as artificial cartilages and tendons, robust antifouling coatings, and hydrogel robots. Inspired by the nanostructured interfaces between tendons/ligaments/cartilages and bones, we report that bonding ordered nanocrystalline domains of synthetic hydrogels on engineering materials can give a fatigue-resistant adhesion with an interfacial fatigue threshold of 800 J m−2, because the fatigue-crack propagation at the interface requires a higher energy to fracture the ordered nanostructures than amorphous polymer chains. Our method enables fatigue-resistant hydrogel coatings on diverse engineering materials with complex geometries. We further demonstrate that the fatigue-resistant hydrogel coatings exhibit low friction and low wear against natural cartilages.

Metodologia prognozowania trwałości zmęczeniowej oraz jej walidacja w oparciu o przyspieszone badania niezawodności dźwigni skoku wirnika nośnego

Because the industrial products have lifetimes, without failing, of up to millions of cycles, it is mandatory that the aerospace field puts into practice the accelerated testing techniques. The lifetime prediction methodology for industrial products presented in this paper was put into practice by performing accelerated reliability testing on an aerospace product (the pitch link of a helicopter). The results showed a significant reduction of the testing time and costs. One important aspect highlighted in this paper is the equivalence between accelerated reliability testing and the traditional reliability testing, by using the two fundamental principles of the accelerated experiments: first, the stresses applied must not alter the physical mechanism through which the defects are produced and second, the conservation of the distribution laws of the failure times. In this way, by equivalence of the accelerated experiments, the methodology contained in this paper was validated.

On the fracture resistance of dragonfly wings

The biological success of insects is attributed to evolution of their wings. Over 400 million years of evolution, insect wings have become one of the most complex and adaptive locomotor structures in the animal kingdom. Although seemingly fragile, they satisfactorily perform their intended function under millions of cycles of repeated stress without failure. However, mechanistic origins of wing resistance to failure remain largely unknown. Most of our understanding of biomechanics of insect wing and flight is based on computer simulations and laboratory experiments. While those studies are needed to reveal certain aspects of wing design, a full understanding can be achieved only by linking obtained data with results of studies in natural conditions. In this study, we tracked the initiation and progression of wing damage of dragonflies in their natural habitats. By quantifying wing area loss over the flight season, we aimed to find a link between the wing structure and accumulated damage. Our results showed that dragonfly wings are exceptionally damage tolerant. Even at the very end of the flight season, the mean wing area loss does not exceed 1.3% of the total wing area. Crack termination, deflection, bifurcation and bridging are the mechanisms that raise the resistance of wings to fracture. This study suggests that insect wings are adapted not only for flight efficiency, but also for damage tolerance. Hence, they should be studied not only from the perspective of aerodynamic performance, but also from that of fracture mechanics.