Influence of Strain Gradient on Fatigue Life of Carbon Steel for Pressure Vessels in Low-Cycle and High-Cycle Fatigue Regimes

This paper discusses how the strain gradient influences the fatigue life of carbon steel in the low-cycle and high-cycle fatigue regimes. To obtain fatigue data under different strain distributions, cyclic alternating bending tests using specimens with different thicknesses and cyclic tension–compression tests were conducted on carbon steel for pressure vessels (SPV235). The crack initiation life and total failure life were evaluated via the strain-based approach. The experimental results showed that the crack initiation life became short with decreasing strain gradient from 102 to 106 cycles in fatigue life. On the other hand, the influence of the strain gradient on the total failure life was different from that on the crack initiation life: although the total failure life of the specimen subjected to cyclic tension–compression was also the shortest, the strain gradient did not affect the total failure life of the specimen subjected to cyclic bending from 102 to 106 cycles in fatigue life. This was because the crack propagation life became longer in a thicker specimen. Hence, these experimental results implied that the fatigue crack initiation life could be characterized by not only strain but also the strain gradient in the low-cycle and high-cycle fatigue regimes.

Competitive Failure of Bolt Loosening and Fatigue under Different Preloads

Existing research on the competitive failure relationship, failure mechanism, and influencing factors of bolt loosening and fatigue under different preloads is insufficient. This study analyzes the competitive failure relationship between bolt loosening and fatigue under composite excitation through competitive failure tests of bolt loosening and fatigue under different preloads. The results indicated that the failure mode of the bolt is only related to the load ratio (R) and is unrelated to the initial preload and excitation amplitude, which only determine the failure life of the bolt. The small axial loads of composite excitation can restrain bolt failure, and the significant degree of this restraining effect is different for different preloads. Subsequently, a fracture analysis of the bolt was performed to verify the competitive failure relationship of the bolt from a microscopic perspective, and the competitive failure mechanism of the bolt was determined. Based on the findings, we propose a calculation equation for the optimal preload of 8.8 grade high-strength bolts that can serve as a reference for engineering applications.

An analytical and probabilistic model with concordance for detecting mine-like objects with mirror symmetry

PurposeThe purpose is to develop search and detection strategies that maximize the probability of detection of mine-like objects.Design/methodology/approachThe author have developed a methodology that incorporates variational calculus, number theory and algebra to derive a globally optimal strategy that maximizes the expected probability of detection.FindingsThe author found a set of look angles that globally maximize the probability of detection for a general class of mirror symmetric targets.Research limitations/implicationsThe optimal strategies only maximize the probability of detection and not the probability of identification.Practical implicationsIn the context of a search and detection operation, there is only a limited time to find the target before life is lost; hence, improving the chance of detection will in real terms be translated into the difference between success or failure, life or death. This rich field of study can be applied to mine countermeasure operations to make sure that the areas of operations are free of mines so that naval operations can be conducted safely.Originality/valueThere are two novel elements in this paper. First, the author determine the set of globally optimal look angles that maximize the probability of detection. Second, the author introduce the phenomenon of concordance between sensor images.

Investigations on the changed intensity shot peening specimens machined from SS304: process characterization, fatigue modeling and failure analyses

Characterization on the surface morphology, residual stress relaxation and fatigue life prediction of the changed intensity shot peening specimens machined from SS304 were carried out. The present work aims, first and foremost, to model the fatigue performance of shot peening specimens machined from SS304 in extra-low-, low- and high-cycle regime by clarifying the relaxation life component and fatigue life component with the total failure life, thereby successfully evaluating the fatigue performance of un-/0.1 mmA-/0.25 mmA-/0.4 mmA-peened components with satisfactory results in the whole cycle regime. It is, therefore, essential to provide a precise definition of the master life diagram on the purpose of evaluating the fatigue performance of shot peening components in service by linear interpolation of shot peening intensities considering the engineering applicability. Additionally, the characterization of multiple-fatigue crack initiation to failure was also identified by fractography analysis, which reasonably illustrated the non-conservative life prediction in the high-cycle regime.

Life Prediction Method of Power Battery for New Energy Vehicle

Battery life is a key factor restricting the development of new energy vehicle manufacturing industry.Taking a LiMn2O4 power battery as an example, the life prediction method of power battery based on performance degradation data was studied. It is found that the capacity of the battery basically conforms to the decline trajectory of the power function, and the pseudo failure life of the battery is extrapolated by using the decline model. The distribution of pseudo failure life is studied, and the results are consistent with the fitting effect of Weibull distribution. Finally, the reliability of the battery is evaluated based on Weibull life distribution. This paper analyzes the influence of the actual cycle data on the prediction accuracy. The test results show that the life model and reliability evaluation method have high accuracy, and solve the problems of long life evaluation cycle and high cost of power battery.

Assessment of Failure Life Evaluation Methods for Structural Discontinuities with Fatigue and Creep-Fatigue Tests on Multi-Perforated Plate Made of Mod.9Cr-1Mo Steel

This study compares and assesses the different fatgue and creep-fatigue life eveluation methods by performing tests of perforated plate made of Mod.9Cr-1Mo steel. Multi-perforated plate was subjected to mechanical cyclic loading at 550°C, and crack initiation and propagation on the surfaces of the holes were observed. A series of finite element analyses (FEA) were carried out to predict the number of cycles to failure by the several failure life evaluation methods, and these predictions were then compared with the test results. Several types of evaluation methods that use the elastic FEA were applied, namely the stress redistribution locus (SRL) method, simple elastic follow-up method. In addition to these, evaluation was also carried out using the results of inelastic FEA to compare these elastic FEA based estimation method. The comparisons indicate that, for all conditions tested, the SRL method provided a rational prediction of the fatigue and creep-fatigue life when ? = 1.6 was applied, where ? = 1.6 is the recommended reduction factor for this method in general use. A comparison of the SRL method and the results of the inelastic FEA indicated that the applicability of the value of factor ? in the SRL method depends on the elastic region remaining in the cross-section including the evaluated point and the spread in the plastically deformed region in the specimen.

Epinephrine soaked tampons induced transient acute dilated cardiomyopathy during FESS procedure

Background Epinephrine, in all modes of use, may pose a wide range of cardiotoxic events, ranging from sinus tachycardia to heart failure, life threatening arrhythmias, and even death. Because of daily and extensive use of epinephrine, these unusual and rare events tend to be forgotten by physicians. We present a case of dilated cardiomyopathy that developed following routine use of epinephrine-impregnated tampons during function endoscopic sinus (FESS) surgery. Case presentation A healthy, 24-year-old man with no family history of heart disease has undergone elective surgery under general anesthesia to repair the paranasal sinuses using endoscopic approach. During surgery, soon after being treated with 1: 1000 diluted epinephrine-soaked tampons, an hypertensive crisis was noticed followed by pulseless electrical activity. An extensive examination led to the diagnosis of non-ischemic dilated cardiomyopathy. After several days of heart failure medical therapy, complete resolution of all structural and functional changes was achieved. Conclusion In our case, we present an unusual and rare event of acute dilated cardiomyopathy following the use of epinephrine-soaked tampons during elective FESS surgery. A prompt response was observed after several days of heart failure treatment. Awareness of the epinephrine cardiotoxic potential even in the form of soaked tampons is essential for proper diagnosis and prompt treatment.