A novel method to improve fatigue behaviors of holed structures based on electromagnetic force

In this study, a novel method stress wave strengthening (SWS) process based on electromagnetic force was proposed to improve the fatigue life of holed structures. Corresponding tests were carried out to explore the fatigue performance of SWS. Cold expansion (CE) was also investigated for comparison. The fatigue life of SWS and CE samples were evaluated, moreover, the mechanisms of fatigue failures and life enhancements were also discussed. Results showed that double-side SWS extended fatigue life significantly and reduced stiffness degradation more effectively with respect to CE process. Moreover, fatigue cracks commonly appeared at mid-planes of hole surfaces and horizontally grew in SWS samples, which differed a lot from CE samples. Through the residual stress measurement, it is seen that more uniform residual stress along axial direction can be obtained by SWS compared to CE, which can explain the fatigue life enhancement and failure mechanism of SWS method.

Investigations on Structural Integrity of Piping Compensators Under Angular Rotational Deformation

The aim of this paper is to investigate the effect of angular rotational misalignment in pipe structure on the deflection based convolution stresses. Such stresses are generated in the thin walled unreinforced bellows compensators during the expansion-contraction function. On the convolution geometry, the most vulnerable stress type is meridional deflection stresses under the internal pressure. Therefore, it’s critical to check the structural integrity of pipe systems with bellows expansion joints, which typically connected to the process equipment’s including boilers, pressure vessels, reactors, heat exchangers, refineries, and so on. The findings of theoretical and experimental investigations of thin-walled unreinforced conditioned bellows subjected to different angular rotations are presented in this paper. The meridional deflection stresses are investigated for the different operating pressures when bellows subjected to angular rotations of 1°, 1.5° and 2° in the flexural plane. In addition, the testing is performed along various longitudinal lines across the periphery of the bellows to determine the maximum induced stress points on the convolution profile. The higher meridional stress is seen to be the bending stress at the bottom curved toroidal section of the convolution, which approaches towards the elastoplastic regime at 1° to 2° of angular deviation in flexural plane. These extreme stress points may prove the risky areas at the root of the convolution for the fatigue failures. Further, the results of the maximal convolution stress assessment are useful in predicting the structural integrity of bellows in elastic regime, when prone to the angular shift.

Failure Modes and Root-Cause Analyses of Advanced Drill-Collar Connections

Summary Advanced drill-collar connections have been developed with 10 times extended fatigue life compared with the corresponding replaced connections. More than 4,000 advanced connections have been run in North America. Although these connections have demonstrated substantial fatigue-strength improvement in operation, some failures have occurred. Multiple failed connection samples have been retrieved and analyzed for their failure modes and the root causes. In the failure analyses, manufacturing data were reviewed to identify any possible discrepancies between design specifications and manufactured components. The field run data were analyzed for the loading histories of the connections. The downhole fluid properties were also reviewed to identify their possible effects on the connection performances. The bottomhole assemblies (BHAs) were numerically analyzed to determine the loading distributions. The failed connection samples were physically processed and inspected in a metallurgical laboratory. Based on the combined numerical and testing analyses, the conclusions on the failure modes and the root causes were drawn. It was found that the primary failure mode for these connections was fatigue. The root causes for the fatigue failures can be divided into two categories: manufacturing causes and operational causes. Among the manufacturing failure causes, incorrect cold rolling is the primary one. The operation-related failures were mainly caused by overloading. Through failure mode and root-cause analyses, the manufacturing and operational related risks for the advanced drill-collar connections were mitigated accordingly. It therefore greatly improved the quality assurance of the advanced connections.

Failures of Mechanical Springs

Mechanical springs are used in mechanical components to exert force, provide flexibility, and absorb or store energy. This article provides an overview of the operating conditions of mechanical springs. Common failure mechanisms and processes involved in the examination of spring failures are also discussed. In addition, the article discusses common causes of failures and presents examples of specific spring failures, describes fatigue failures that resulted from these types of material defects, and demonstrates how improper fabrication can result in premature fatigue failure. It also covers failures of shape memory alloy springs and failures caused by corrosion and operating conditions.

Appraising Pavement Surface Distresses And Expected Mitigation Measure On Selected Road Segment

The work visually inspects and evaluate the pavement failures and their causes as well as resolution methods. It is quite important to examine and identify the causes of the failed pavement to select a proper treatment option. The study consisted of two tasks: the first covers the detail visual inspection of the existing pavement failures, whereas the second investigates the actual causes of these failures. From Areka to Wolaita Sodo was selected for investigation. An intensive field work was carried out on the existing pavement condition of this road. It was found that most of the damaged pavement sections suffered from severe cracking, potholes and raveling failures. These failures might have been caused by fatigue failures on pavement structure due to the movement of heavily loaded truck – trailers. The damage could also be attributed to poor drainage, inadequate design and improper pavement materials.

Consistent inconsistencies in braking: a spatial analysis

The dynamic system that is the bipedal body in motion is of interest to engineers, clinicians and biological anthropologists alike. Spatial statistics is more familiar to public health researchers as a way of analysing disease clustering and spread; nonetheless, this is a practical approach to the two-dimensional topography of the foot. We quantified the clustering of the centre of pressure (CoP) on the foot for peak braking and propulsive vertical ground reaction forces (GRFs) over multiple, contiguous steps to assess the consistency of the location of peak forces on the foot during walking. The vertical GRFs of 11 participants were collected continuously via a wireless insole system (MoticonReGo AG) across various experimental conditions. We hypothesized that CoPs would cluster in the hindfoot for braking and forefoot for propulsion, and that braking would demonstrate more consistent clustering than propulsion. Contrary to our hypotheses, we found that CoPs during braking are inconsistent in their location, and CoPs during propulsion are more consistent and clustered across all participants and all trials. These results add to our understanding of the applied forces on the foot so that we can better predict fatigue failures and better understand the mechanisms that shaped the modern bipedal form.

Quantification of vertical, lateral, and longitudinal fastener demand in broken spike track: Inputs to mechanistic-empirical design

To address a recent challenge related to broken spikes in premium elastic fastening systems that have led to at least ten derailments and require manual walking inspections as well as build upon mechanistic-empirical (M-E) design principles for future fastening system component design, this paper quantifies the vertical, lateral, and longitudinal fastening system loads under revenue service traffic in a curve that has regularly experienced spike fastener fatigue failures. Previous data has indicated that the high rail of Track 3 experienced the most failures at this location. The data from this investigation sheds light into why failures are more predominant at this location than others and how the vertical, lateral, and longitudinal loads cannot be considered independently. Specifically, while the magnitude of the applied loading was the lowest on the high rail of Track 3, the threshold for failure was also the lowest given the operations at this location led to unloading of the high rail, thus indirectly highlighting the importance of friction within a fastening system. The data also show the high rail of Track 3 was subjected to the highest L/V load ratios and was an outlier in the typical lateral load reversals applied likely leading to spike stress reversals and thus a shorter fatigue life. Finally, based upon the data, it is recommended that to mitigate spike failures, as well as similar fastener challenges in other track types (e.g. rail seat deterioration, etc.) railroads should ensure trains operate close to the balance speed and use fastening system that transfer loads through friction. This study also provides novel data for M-E design of fastening systems.

An Alternative Carcass Design to Prevent Flow-Induced Pulsations in Flexibles

Flow-induced pulsations (FLIP) are pressure oscillations generated inside of flexibles used in dry gas applications that can cause unacceptable vibration levels and eventually failure of equipment. Because of the design of inner layer of the flexibles, the carcass, the frequency of the pulsations is high, potentially leading to fatigue failures of adjacent structures in a relatively short time. The traditional carcass is made of a steel strip formed into an interlocked s-shape in a series of preforming and winding steps. To enable bending of the pipe, gaps are present between each winding with a shape that can cause FLIP. The gaps can be reduced, and the profiles optimized, but they will always be able to generate FLIP at a certain gas velocity. To remove the risk of FLIP in dry gas projects and ensure that operator does not get operational constraints, an alternative carcass design has been developed. This is essentially a conventional agraff carcass but with an additional cover strip to close the gap, making the resulting carcass nearly smooth bore in nature. With a smooth bore this carcass can be used for flexibles which have a risk of FLIP or to produce pipes with a lower internal roughness. This alternative design can be manufactured and can therefore build on the large manufacturing and design experience of the traditional strip carcass. This alternative carcass technology is to undergo a full qualification process, in which the risk of flow induced pulsations is an essential component. With the investigated alternative carcass design, the cavities present in the traditional agraff designs are covered. It is expected that the risk due to the appearance of FLIP is therefore eliminated. Theoretical analysis, numerical simulations and scaled experiments are used to explore the risk for the alternative technology to create FLIP. The theoretical analysis is based on existing knowledge and literature. The numerical simulations and scaled tests are done to generate direct evidence for the end statements resulting from the qualification process. Numerical simulations follow the power balance method presented by the same authors in earlier papers. The same applies to the techniques used for the scaled tests. The main outcome of the qualification presented here are the pressure drop performance and the anti-FLIP capabilities of the design. The new design performs significantly better than the nominal design carcass for the same purpose. The pressure drop coefficients found are close to those expected for a normal, non-corrugated pipe, and thus the recommendation given by the API 17J standard does not apply to this design. The pressure drop coefficient is dependent on the installation direction of the flexible with respect to the flow. No signs of FLIP are found for the nominal design of the investigated carcass technology. This is the case for either installation direction. This is explained from a theoretical point of view, but also numerical and experimental evidence are provided.

Vibration Fatigue Assessment of Additive Manufactured Nickel Alloy with Inherent Damping

The fatigue life behavior and internal surface conditions of inherently damped Additive Manufactured (AM) specimens subjected to vibration bending are under investigation. This study supports research that demonstrated 95% vibration suppression due to damping capability of AM components with 1-3% internal volume of unfused powder. The damping demonstrations have been carried out using laser powder bed fusion (LPBF) specimens of various thicknesses, lengths, and unfused internal powder configurations. In addition, damping is shown to be achievable with both nickel-based alloys and stainless steel specimens. Despite the promise of this method, the viability of fatigue performance is unknown. The following effort aims to address this structural integrity issue; specifically, this study explores whether internal pocket roughness or erosion caused by powder particle motion induces a fatigue life debit. These concerns are addressed by comparing the fatigue behaviors of unfused powder pocket and fully-fused nickel based alloy 718 specimens. Microscopy results confirmed a long suspected powder interaction phenomena as well as appearances of erosion. Furthermore, fractography supports that fatigue failures initiate near the surface of maximum strain/stress at porous features consistent with stock (non-optimized) LPBF process parameters.

Effect of Longitudinal Fastener Stiffness on Fastening System Loading - Initial Findings

Over the past 20 years, there have been at least 10 derailments due to spike fatigue failures in North America. Researchers believe that fatigue failure is caused by a combination of lateral and longitudinal spike loading. The literature indicates the vertical load and fastener friction must be considered when estimating failure locations. Though the in-track vertical, lateral, and longitudinal fastener forces have been quantified at a location that has experienced spike failures, there is a need to account for additional fasteners and track locations. Fastening systems can affect track stiffness, thus, laboratory experimentation was performed to quantify stiffness of multiple fastening systems. This data was input into an analytical model which quantified the effect of stiffness on longitudinal fastener loading. The data indicate there is significant variance in fastening system stiffness within, and between, systems. However, this variation in fastener stiffness has a reduced effect on the load transferred to the fastening system. More work is needed to validate this in the lab or field given variability within a system could lead to stress concentrations that are not fully captured using the current idealized analytical method.