Cyclic Bending Stress Research Articles

Qualification of Austenitic Stainless Steels for the Development of Load-Sensitive Material Sensors

To detect mechanical overloads on the component directly in operation, a metastable material can be used as a load-sensitive sensor when combined with an eddy current testing system. In order to find a suitable metastable sensor material that exhibits microstructural changes at an early stage before fatigue failure, quasi-static tensile tests and cyclic rotating bending tests were carried out with the austenitic stainless steels 1.4301 (2 batches), 1.4305, 1.4541 and 1.4550. For the detection of microstructural changes, electromagnetic testing was used in-situ in the tensile test and ex-situ between the rotating bending test after a pre-defined number of cycles. The investigated materials 1.4301 batch2 and 1.4550 showed the largest signal changes and the lowest austenite stability both in the tensile test and under cyclic bending load. Due to the better mechanical properties, 1.4301 batch2 should be preferred. The order of the austenitic stainless steels tested was similar in terms of transformation behavior in both tests. Thus, the tensile test combined with in-situ electromagnetic testing appears to have potential as a suitable benchmark test for austenite stability. With regard to the cyclic bending stress, an overload of the specimens could be detected for the materials 1.4301 batch2, 1.4305, 1.4541 and for the 1.4550 on the basis of a significant amplitude change. At low bending stresses, uncritical for structural integrity, no increase in amplitude was measured. The results have shown that an early detection of overloads is possible with several materials, however, the potential for detecting overloads varies between materials and also between individual batches. In addition, it has been observed that as the bending stress increases, the gradient of the change in amplitude over the number of cycles increases as well. Thus, with a known number of cycles, it could be possible to classify the previous load spectrum based on the difference in amplitude between two measurements.

The influence of mechanical cyclic bending stress on the reliability of the emerging DDR5 memories in the industrial market

The influence of mechanical cyclic bending stress on the reliability of the emerging DDR5 memories in the industrial market

Copper Nanowire/Polydopamine-Modified Sodium Alginate Composite Films with Enhanced Long-Term Stability and Adhesion for Flexible Organic Light-Emitting Diodes.

Copper nanowire (CuNW), with combined advantages of high conductivity and cost-effectiveness, is considered a promising material for the development of next-generation transparent conductive films (TCFs) in the field of flexible optoelectronics. However, the practical application of CuNW TCFs is hindered by some limitations, such as conductivity degradation and poor adhesion. Here, we demonstrate a stable CuNW composite film by embedding CuNWs into a polydopamine (PDA)-modified sodium alginate (NaAlg) matrix without sacrificing the optoelectronic properties of the CuNW network. The introduction of the PDA modifier significantly enhances the antiaging capability of the NaAlg layer, providing strengthened protection of the embedded CuNWs against moisture and oxygen, thereby resulting in minimal degradation of the conductivity of CuNWs for up to 9 months under ambient conditions. Simultaneously, the interface adhesion between the CuNW network and the substrate is further enhanced due to the abundance of catechol structures in PDA, allowing for the maintenance of the electrical conductivity of the CuNW network even under cyclic external bending stress and tape-peeling forces. In addition, embedding CuNWs into the polymer binding layer produces a CuNW composite film with a very smooth surface. A flexible OLED based on the PDA-modified NaAlg/CuNW TCF is successfully fabricated, exhibiting performance comparable to that of a traditional rigid indium tin oxide-based device, while also demonstrating remarkable mechanical durability. The modification strategy can promote practical applications of the CuNW network in flexible optoelectronic devices.

Novel Reliability Method Validation for Floating Wind Turbines

Wind turbines and associated parts are susceptible to cyclic stresses, including torque, bending, and longitudinal stress, and twisting moments. Therefore, research on the resilience of dynamic systems under such high loads is crucial for design and future risk‐free operations. The method described in this study is beneficial for multidimensional structural responses that have undergone sufficient numerical simulation or measurement. In contrast to established dependability methodologies, the unique technique does not need to restart the numerical simulation each time the system fails. Herein, it is demonstrated that it is also possible to accurately predict the probability of a system failure in the event of a measurable structural reaction. In contrast to well‐established bivariate statistical methods, which are known to predict extreme response levels for 2D systems accurately, this study validates a novel structural reliability method that is particularly suitable for multidimensional structural responses. In contrast to conventional methods, the novel reliability approach does not invoke a multidimensional reliability function in the Monte Carlo numerical simulation case. As demonstrated in this study, it is also possible to accurately anticipate the likelihood of a system failure in the case of a measurable structural reaction.

Oligodendrocyte tethering effect on hyperelastic 3D response of axons in white matter

A novel finite element model is proposed to study the mechanical response of axons embedded in extracellular matrix when subjected to tensile loads under purely non-affine kinematic boundary conditions. Ogden hyperelastic material model describes the axons and the extracellular matrix material characterizations. Two axon-glia tethering scenarios in white matter are studied a single oligodendrocyte (single-OL) with multiple connections a multi-oligodendrocyte (multi-OL) one. In the multi-OL tethering configuration, resultant forces are randomly oriented as distributed glial cells arbitrarily wrap around axons in their immediate vicinity. In the single-OL setup, a centrally located oligodendrocyte myelinates multiple axons nearby. Tethering forces are directed towards this oligodendrocyte, resulting in greater directionality and farther-reaching stress distribution. The oligodendrocyte connections to axons are represented by a spring-dashpot model. The material properties of myelin served as the upper limit for the parameterization of the oligodendrocyte stiffness (“K"). The proposed FE models enable realization of connection mechanisms and their influence on axonal stiffness to determine resultant stress states accurately. Root mean square deviation analysis of stress-strain plots of different connection scenarios reveal an increasing axonal stiffness with increasing tethering, indicating the role of oligodendrocytes in stress redistribution. In single-OL submodel, for the same number of connections per axons, RMSD values increased as “K" (the oligodendrocyte spring stiffness) values were set higher. RMSD calculations reveal that for a “K" value, single-OL model yielded slightly stiffer models compared to multi-OL. The current study also addresses the potential geometrical limitations of multi-OL model by randomizing and adding connections to ensure greater responsiveness. Cyclic bending stresses noticed in both submodels suggest the risk of axonal damage accumulation and repeated load failure.

Wearable nitrogen oxide gas sensors based on hydrophobic polymerized ionogels for the detection of biomarkers in exhaled breath

High-performance chemical sensors can be used for detecting biomarkers in exhaled breath. The use of chemiresistive-type gas sensors has been limited because of their ineffective feasibility and relatively poor operational stability against humidity and physical deformations. In this study, wearable chemiresistive-type gas sensors based on bar-printed ionogels are developed for the detection of nitrogen oxide (NOx) at ppb levels. The ionogels consist of polymerized ionic liquids (ILs) incorporated into a carefully chosen hydrophobic polymer matrix. The proposed sensors exhibit a sensitive response of 11% when exposed to 300 ppb of NOx target gas for 15 s of exhaled breath duration and an outstanding recovery of up to 100% for 25 s of inhaled breath duration. Furthermore, high-performance ionogel-based biosensors exhibited a theoretical detection limit of 0.11 ppb and an excellent selectivity toward different oxidizing and reducing gases. To realize practical biosensor applications, the effects of humidity in exhaled breath at different temperatures and the mechanical stability against cyclic bending stress on the sensing performance are investigated. Highly stable sensing performances were achieved under harsh conditions with a relative humidity of 90% at 45 °C for 30 days, even under a bending state measured and 20,000 bending cycles at a strain of 30%. Finally, the sensing mechanism of the chemiresistive-type gas sensors and the origin of their high sensitivity and stability are investigated by analyzing the interactions between ion pairs of the ILs and NOx molecules, as well as the incorporation of ILs into the hydrophobic polymer matrix.

Highly Flexible and Durable Thermoelectric Power Generator Using CNT/PDMS Foam by Rapid Solvent Evaporation.

Using a simple, rapid solvent evaporation process, the authors produced 3D carbon nanotube (CNT)/polydimethylsiloxane (PDMS) foams with both high thermoelectric (TE) and good mechanical performance and used them to fabricate highly flexible and durable TE generators. The numerous pores and interfaces in the CNT/PDMS foams, which have porosities exceeding 87%, afford very low thermal conductivity of 0.13 W m-1 K-1 . The foam has a zT value of 6.6 × 10-3 , which is twice as high as that of pristine CNT foam. Importantly, the CNT/PDMS foam exhibits good tensile strength of 0.78MPa, elongation greater than 20%, and excellent resilience even at compressive strain of 80%. This foam is used to fabricate a highly flexible TE foam generator that exhibits a moderate output power of 1.9 µW generated from the large temperature gradient of 18.1 K produced by applied heat. The authors also demonstrate a practical TE foam generator that produces sustainable output power of 3.1 µW under a compressive strain of 80% and 38.2 nW under the continuous vibrational stress produced by a car engine. The TE foam generator also exhibits excellent stability and durability under cyclic bending and harsh vibrational stress.

Electrical and cyclic bending properties of screen-printed conductive patterns containing different ratios of silver microparticles and silver microflakes

Silver microparticles (Ag MPs) are widely used in conductive pastes for printed flexible electronics because of their easier synthesis and lower cost than silver nanoparticles. However, the cyclic bending reliability of the printed conductive patterns containing Ag MPs needs to be improved to use the devices under bending conditions. In this work, the conductive paste was prepared by mixing two silver pastes containing silver microparticles and silver microflakes (Ag MFs). These mixed pastes were screen-printed on PEN films to fabricate conductive patterns. Although the electrical resistivity increased 3.7 times as the Ag MFs content increased from 0 to 30 wt%, the bending stability was improved by Ag MFs in conductive patterns because the formation of crack under cyclic bending stress was suppressed. The increase of the resistivity was due to decreasing the number of electrical contacts caused by the formation of voids within the patterns containing a large amount of Ag MFs. These results are useful for designing printed conductive metal patterns with high bending stability.

Tribo-fatigue characteristics of braided wire rope for traction under low cycle bending fatigue

Braided wire rope as the traction tool is indispensable for stringing conductors in overhead transmission lines. However, rope body wear and fatigue fracture failure often lead to its premature scrap. In this paper, the bending fatigue test of YS 9-8 × 19 braided wire rope for traction was carried out by the test rig. The bending fatigue life of the braided wire rope was discussed by the number of broken wires. Furthermore, the fracture mechanism and wear morphology of the rope wires were analyzed by Ultra-depth three-dimensional microscope combined with the scanning electron microscope. The fatigue damage mechanism was discussed, and the tribo-fatigue characteristics of the wire rope were investigated. Results show that the failure of braided wire rope is the result of the interaction of cyclic bending stress and surface damage. Moreover, most broken wires occur at the place where the rope wires are severely worn. When the bending fatigue cycle is between 2.0 × 104–2.4 × 104, the number of broken wires reaches the scrap standard. Additionally, the bending tribo-fatigue damage of the wires between adjacent strands is the most serious. The primary wear mechanisms of the wires in contact with the pulley are fatigue wear and abrasive wear. In contrast, the wires between adjacent strands are affected by fatigue wear, adhesive wear, and tribo-oxidation.

Failure analysis and countermeasures of the SCM435 high-tension bolt of three-step injection mold

PurposeThe objective of this study was to perform damage analysis of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine.Design/methodology/approachDamage material used in this study was a SCM435 high-strength bolt connecting upper and lower molds of a three-stage injection mold. Causes of damage were determined by macroscopic observation. Microstructure observation was done using a metallic microscope, scanning electron microscope (SEM, S-2400, HiTachi, Japan), energy dispersive X-ray spectroscopy (EDS, Kevex Ltd., Sigma) and Vickers hardness tester (HV-114, Mitutoyo). Fatigue limit of the damaged material was evaluated using equivalent crack length.FindingsBolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. The damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment. Screws require compression residual stress due to peening.Originality/valueThis study conducted failure analysis of damaged SCM435 bolts connecting upper and lower parts of the three-stage injection mold. Fatigue limit of the damaged material was evaluated using equivalent crack length. In order to control this fracture, accurate tightening of bolts, accuracy of heat treatment and screws are required for compression residual stress due to peening.

Analysis of fatigue behaviour of drill pipe on pin-box connection

Drilling is one of the costliest and risky activities in oil and gas industry due to complexity of interactions with downhole formation. Cyclic loads while drilling cause the initiation and growth of cracks in oil tubulars. This phenomenon, known as fatigue, results in permanent reduction of the failure-free service envelope of a certain tubular. Further, most of the drill string failures are triggered by fatigue, which results from repetitive cyclic bending loads and stresses in tensile or buckled drill strings. Fatigue is a cumulative and non-reversible condition induced by repetitive cyclic bending loads and tensile or buckled drill pipe stresses. Fatigue exists even though cyclic tension of the drill pipe material is much lower than static strength limit. Present work investigates fatigue capacity of the 4” WT38 drill pipe connection where cracks have been observed. In accordance with the geometry of connection, a hot spot stress from bending moment is calculated in the crack location in the first thread (upper) of the pin. The DNVGL-RP-C203 SN-curve B1 “in air” is used as relevant fatigue SN curve for the drill pipe thread location. Finite element method (FEM) is employed in modeling and analyzing of drill pipe on pin-box connections. With this method, various connections can be investigated relatively faster and cheaper compared with experimental tests. It is found that the fatigue failure may have been caused as a result of the cyclic load level and number of load cycles. A detailed discussion of the fatigue damage assessment concludes the paper.

Fatigue behavior of PLA-wood composite manufactured by fused filament fabrication

In this paper, the fatigue behavior of a polylactic acid-based composite reinforced with wood (trademarked as Timberfill) processed through fused filament fabrication is analyzed through rotating bending fatigue tests. Originally, this material was developed with the aim of enhancing the resistance of PLA by increasing the inner friction between polymer filaments. This work aims to confirm whether the inclusion of wood delivers the expected mechanical advantages from a functional point of view. The effect of wood on the mechanical behavior of the material is also assessed by comparing the results to similar experimental observed on non-reinforced PLA specimens. Firstly, the optimal set of parameters and levels resulting in the highest number of cycles to failure are determined, and compared to those found for PLA, by applying a Taguchi L27 experimental array. Layer height, infill level and nozzle diameter prove to be the most influential parameters on fatigue life. During a second phase, a set of specimens manufactured through the best parameter set were tested at different stress levels to represent the S-N curve. Infinite life was observed for specimens loaded with a maximum stress of 17.9 MPa. Therefore, this value can be considered as a lower threshold of the endurance limit for Timberfill cylindrical parts subjected to cyclic bending stress. SEM observations reveal that wood has a detrimental effect on the PLA matrix, as is reduces the cohesion of deposited filaments, and increases the ductile behavior of the base material.

Fracture failure analysis of coal mill shaft

During the operation of No.2 boiler in a power plant, the fracture of a coal mill shaft occurred. The fracture causes of the coal mill shaft were found by macroscopic inspection, metallographic inspection, chemical composition analysis, fracture morphology analysis and mechanical property inspection. The experimental results showed that: 1. The external surface of the coal mill shaft had been welded, and the poor welding process resulted in a large number of welding defects such as cracks, slag inclusions and lack of fusion in the overlaying layer; 2. The improper hot working process of the coal mill shaft resulted in the abnormal metallographic structure of the shaft, and the existence of serious reticulated ferrite and brittle widmanstatten structure resulted in the low strength of the shaft. 3.Because of the existence of the cyclic torsion and bending stress of large load, the initial crack source occurred at the welding position of the hardfacing layer, and then extended in the form of fatigue, eventually causing the coal mill shaft to break. Three factors led the high cycle and low stress fatigue fracture of the coal mill shaft.

Fatigue life of thermoset composite materials

This article deals with the lifetime of laminated materials produced by different production technologies (hand lamination technology, vacuum bagging technology and prepreg technology with curing in the oven) during cyclic repeated bending stress. Like tested materials composite systems were chosen composite systems with epoxy matrix and carbon reinforcement (Kordcarbon CC200T, epoxy resin with trade name L285) and second composite epoxy system with glass reinforcement (Quadra-axial glass fabric, named Saertex Q-E-820, epoxy resin Biresin CR 82 and third prepreg systems (unidirectional prepreg, trade name Deltapreg VV430U-DT860W-39% and prepreg system with glass fabric VV320P_DT806R-37%). Fatigue tests were performed by cyclic bending loads during a three-point arrangement on a universal servo-hydraulic testing machine INSTRON 8871. Experimentally the number of cycles fracture of the material was determined at 90 % and 80 % of the maximum breaking load.

Stress relaxation in LTPS TFT backplane by architecture modulation on plastic

The effect of structural design on inorganic backplanes was discussed to achieve highly bendable characteristics for flexible electronic applications. Based on a low-temperature polysilicon (LTPS) thin-film transistor backplane, the failure mechanics and tolerance of structures were implemented as a function of backplane geometry and stress value. Results showed that the strain resistance increased in the thin-film backplane by adopting island geometry under bending stress, which was against the fatigue formation with enhanced resilience. The electrical integrity of transistors was achieved at the bending radius of a few millimeters for an island backplane architecture, and the conventional structured inorganic backplanes underwent a significant change in electromechanical feature under the mechanical cyclic bending stress. The stress analysis on the bended surface and the stability behaviors of plastic backplanes embedded in different configurations also showed that the mesh-like islanded geometry in a bending system willingly helped to release the accumulated sheer stress in the thin films.

Failure analysis of a crankshaft of a helicopter engine

A detailed analysis of a crankshaft failure belonging to a helicopter engine is presented. The main objective of this work was to analyze the characteristics of the failure and determine the root cause of the failure of the crankshaft. In order to determine the causes of the crankshaft failure, a material analysis was performed, followed by a detailed observation of the failure mechanisms through macroscopic, microscopic and microstructural examinations of the fracture surface. A preliminary observation of the fractured crankshaft indicates that this failure occurred by a fatigue process where the fracture surface shows obvious signs of cyclic propagation mechanisms. The existence of a large number of beachmarks indicates significant crack growth characterized by the effect of successive starts and stops of the engine by the operating conditions. These beachmarks cover about two-thirds of the total area of the fracture surface and the uniform geometric pattern of the crack front, along the entire propagation zone, allows to conclude that the fatigue process occurred from a loading state consisting essentially of cyclic bending stresses between the crankweb and the main journal of the crankshaft. No original defect was observed either on the surface or inside the material that could be the source of the crack initiation and growth and subsequent final fracture of the component. The analysis of the shell bearings applied to the main journal revealed a significant damage, with fractured location lugs, that are believed to be at the origin of the crack initiation of the crankshaft.

Quantitative monitoring of brittle fatigue crack growth in railway steel using acoustic emission

Structural degradation of rails will unavoidably take place with time due to cyclic bending stresses, rolling contact fatigue, impact and environmental degradation. Rail infrastructure managers employ a variety of techniques and equipment to inspect rails. Still tens of rail failures are detected every year on all major rail networks. Inspection of the rail network is normally carried out at night time, when normal traffic has ceased. As the implementation of the 24-h railway moves forward to address the increasing demand for rail transport, conventional inspection processes will become more difficult to implement. Therefore, there is an obvious need to gradually replace outdated inspection methodologies with more efficient remote condition monitoring technology. The remote condition monitoring techniques employed should be able to detect and evaluate defects without causing any reduction in the optimum rail infrastructure availability. Acoustic emission is a passive remote condition monitoring technique which can be employed for the quantitative evaluation of the structural integrity of rails. Acoustic emission sensors can be easily installed on rails in order to monitor the structural degradation rate in real time. Therefore, apart from detecting defects, acoustic emission can be realistically applied to quantify damage. In this study, the authors investigated the performance of acoustic emission in detecting and quantifying damage in rail steel samples subjected to cyclic fatigue loads during experiments carried out under laboratory conditions. Herewith, the key results obtained are presented together with a detailed discussion of the approach employed in filtering noise sources during data acquisition and subsequent signal processing.

Downhole vibration causing a drill collar failure and solutions

In large borehole drilling of some blocks or formations, due to serious downhole vibration, fatigue failure of a drill collar occurs frequently and most washouts and fractures are in thread root. An analysis of the above failure shows that the drill collar fatigue failure is caused by the cyclic bending stress due to serious downhole vibration. Therefore, downhole vibration modes were theoretically analyzed in terms of axial vibration, lateral vibration, stick-slip, and the physical model established by the mechanical vibration field. Then the resonance damage caused by the actual different downhole vibrations and its theoretical basis were analyzed; and according to the downhole drill string lateral vibration and whirling law, the best area to ensure drilling parameter stability based on the given boundary conditions was figured out, and the theory was clarified that in the best area of drilling, the maximum ROP will be achieved by maintaining the drill string stable or eliminating the vibration/stick-slip, meanwhile the stress fatigue of BHA will be reduced or eliminated especially for drill collar. Finally, solutions were provided as follows: (1) According to the special BHA, drilling conditions, together with physical and mathematical models listed above, downhole resonance speed and related parameters to be avoided can be easily figured out. It was also clarified that resonance speed is exactly the vibration speed that need to be avoided; and that the resonance frequency can be avoided with software for vibration analysis in BHA design and application at well sites; (2) V-Stab is a new and efficient tool which can reduce or eliminate downhole lateral vibration and stick-slip.

Application of rod mechanics fundamentals for analysis of stress-strain state of the tubing

A method for analysis of stress-strain state of the tubing column in the spatially curved well section with an arbitrary intensity of changes as the zenith and azimuth angle is developed in the article.Stresses and strains are calculated using the rod mechanics fundamentals. The system of vector differential equilibrium equations in the projections on the axes of the moving coordinate system is used for the analysis of elastic equilibrium of the tubing axis.The analysis is carried out by solving the direct problem of the rod bending by means of iterative numerical method implemented in software-oriented mathematical environment.A method to account for the limiting effect of the well walls to move of the elastic tubing axis is provided based on the processing of its geometrical parameters, as well as data and directional survey and profilometric research of the well bore.Using the designed calculation schemes, it is found that local bend of the well axis substantially increases the bending stress, which can reach the yield strength of the tubing material. For example that discussed in the article, the bending stress is approximately 300 MPa, while the minimum yield strength of steel, which are made tubing, is equal to 379 MPa.Moreover, the axial force change caused by the reciprocating motion of a rod suspension may initiate the occurrence of cyclic bending moments and stresses in the tubing. So, for the considered operating conditions, we received the following: the minimum stress of the cycle σmin = 303 MPa; the maximum stress of the cycle σmax = 346 MPa; stress amplitude of the cycle σa = 43 MPa; loading cycle asymmetry factor Rσ = 0,88. This load pattern allows to speak about the cyclic fatigue of the tubing.

Highly bendable characteristics of amorphous indium–gallium–zinc-oxide transistors embedded in a neutral plane

The electromechanical response of an amorphous indium–gallium–zinc-oxide (a-IGZO) thin-film transistor (TFT) fabricated on a polyimide substrate was investigated as a function of the neutral axis location and strain history of the bending system. Here, we demonstrate the pronounced bending characteristics of a-IGZO TFTs and their backplane under extreme mechanical strain when they are embedded in a neutral plane (NP). After being subjected to tensile stress, the devices positioned near the NP were observed to function well against a cyclic bending stress of 2 mm radius with 100,000 times, while TFTs farther from the neutral surface exhibited modified electrical properties.