Initiation Life Research Articles

Framework for Design and Construction of Long-Life Concrete Pavements

In the past, concrete pavements were routinely designed and constructed to provide low-maintenance service life of 20 to 25 years. In fact, the majority of the U.S. interstate and the primary system were designed on the basis of the 20 to 25 year initial service life. Experience has shown that pavements in high volume traffic corridors need to be designed and constructed to provide longer service life because of the difficulties in performing effective repair and rehabilitation activities along these high volume highway corridors. In addition, the public is no longer tolerant of frequent extended lane closures to perform repair activities. It is becoming an established practice in the U.S. to require that concrete pavements provide low-maintenance service life of 40 plus years. PCC pavements can meet this specific requirement if proper considerations are incorporated in the design and good construction practices, including use of sound concrete making materials, are followed. This paper provides an overview of current U.S. practices and efforts at optimizing pavement design features and construction practices to minimize early age failures and provide long-term low-maintenance service in excess of 40 plus years. The paper also provides a framework for ensuring that the critical design and construction features that impact long-term service are recognized and accounted for. The design and construction features discussed include features that improve slab cracking and deflection responses, features that minimize maintenance operations, and construction features that assure long-life pavement.

Fatigue Experiment and Failure Mechanism Analysis of Aircraft Titanium Alloy Wing-Body Connection Joint.

Taking the titanium alloy wing-body connection joint at the rear beam of a certain type of aircraft as the research object, this study analyzed the failure mechanism and verified the structural safety of the wing-body connection joint under actual flight loads. Firstly, this study verified the validity of the loading system and the measuring system in the test system through the pre-test, and the repeatability of the test was analyzed for error to ensure the accuracy of the experimental data. Then, the test piece was subjected to 400,000 random load tests of flight takeoffs and landings, 100,000 Class A load tests, and ground-air-ground load tests, and the test piece fractured under the ground-air-ground load tests. Lastly, the mechanism analysis and structural safety verification of the fatigue fracture of the joints were carried out by using a stereo microscope and scanning electron microscope. The results show that fretting fatigue is the main driving force for crack initiation, and the crack shows significant fatigue damage characteristics in the stable growth stage and follows Paris' law. Entering the final fracture region, the joint mainly experienced ductile fracture, with typical plastic deformation features such as dimples and tear ridges before fracture. The fatigue crack growth behavior of the joint was quantitatively analyzed using Paris' law, and the calculated crack growth period life was 207,374 loadings. This result proves that the crack initiation life accounts for 95.19% of the full life cycle, which is much higher than the design requirement of 400,000 landings and takeoffs, indicating that the structural design of this test piece is on the conservative side and meets the requirements of aircraft operational safety. This research is of great significance in improving the safety and reliability of aircraft structures.

Propagation of a Fatigue Crack Through a Hole.

The stop-hole technique is a well-known strategy to extend the fatigue life of cracked components. The ability to estimate fatigue life after the hole is important for safety reasons. The objective here is to develop strategies for the accurate prediction of initiation and propagation life ahead of the stop-hole. Experimental work was developed in a Compact-Tension (CT) specimen made of 7050-T7451 aluminium alloy and with a 3 mm diameter hole. A total number of 625,000 load cycles were required to re-initiate the crack after the hole. Crack initiation life after the hole was estimated using the Theory of Critical Distances combined with the Smith-Watson-Topper parameter. A value of a0 = 31.83 µm was obtained for El Haddad parameter, which was used to define the critical distance. The predicted life was found to be only 4% lower than the experimental value. The fatigue crack growth (FCG) rate was calculated using a node release strategy, assuming that cyclic plastic deformation is the main damage mechanism and that cumulative plastic strain is the crack driving parameter. A good agreement was found between the numerical predictions of da/dN and the experimental results. The main result, however, is the proposed methodology, which allows predicting the initiation and propagation lives in notched components.

Applicability of fatigue design recommendations for thin plate welded joints by assessment of fatigue crack initiation and propagation life

Applicability of fatigue design recommendations for thin plate welded joints by assessment of fatigue crack initiation and propagation life

Long-term effectiveness of vegetable-based rejuvenation agents across different aging stages of asphalt pavements

ABSTRACT The effectiveness of rejuvenation agents in reducing the stiffness of aged binder in Reclaimed Asphalt Pavement (RAP) material during the initial service life is well documented. However, their long-term efficacy remains under evaluation. This is partially due to the wide variety of rejuvenation agents, with varying chemical compositions, which impact the short- and long-term performance of the rejuvenated material. This paper addresses this concern by assessing the effectiveness of five types of vegetable-based rejuvenation agents across the ageing stages of asphalt mixtures during the service life of flexible pavements. The evaluation includes monitoring the rheological, chemical and performance-related properties of the rejuvenated binder blends (i.e., a combination of aged asphalt binder, virgin asphalt binder and rejuvenator) as ageing progresses. The results indicate that the benefit of rejuvenation decreases with time and that this reduction is a function of the type of rejuvenator. These results highlight that an appropriate selection of a rejuvenator should consider not only the improvement of the material during the production of the mixture and a good response and performance in the initial stage of the pavement operation, as is often the case, but also its capability to maintain these positive effects in later stages of its service life.

Natural history of cyclical parthenogenesis of aphids (Homoptera: Aphidinea)

The article puts forward and argues the hypothesis of the emergence of cyclical parthenogenesis in aphids as a consequence of their ancestral habitation in closed strobiloid galls on coniferous trees. The period of gall opening is greatly extended in time, which prevents normal panmixia in the population and creates a selective advantage for parthenogenetic reproduction. Migration of aphids to secondary host plants, on which closed galls never form, parthenogenetic reproduction on these plants, and the subsequent simultaneous return of “remigrants” to the main host plant make it possible to synchronize the development of the bisexual generation and achieve mass panmixia only at the end of the life cycle, which coincides with the end of summer growth shoots or the autumn end of the vegetation period as a whole. Due to the fact that the development of the bisexual generation always necessarily occurs in the second half of the year, when the conditions for aphid feeding on arboreal plants become unfavorable, small size of sexual individuals and their reduced fertility (often only one egg per female), in comparison with parthenogenetic generations of the first half of the year, are understandable. The evolutionary transition of aphids from conifers to angiosperms in the Cretaceous period in parallel meant the possibility of development in more spacious galls accommodating several consecutive parthenogenetic generations, the transition to viviparity and telescopic embryonization, significantly accelerating the change of generations. The loss of ovipositor in Phylloxeridae and in hypothetically descended from them Aphidoidea can be explained by the initial life in galls, where egg laying does not require specialized ovipository organs. The evolutionary transition from oviparity of parthenogenetic generations to viviparity probably occurred in the ancestors of modern Eriosomatidae, as evidenced by the plesiomorphic features of the reproductive biology of the latter.

Influence of surface integrity on short crack growth behavior in HFMI-treated welded joints

This study investigates the influence of surface integrity and the localized fatigue phenomena on the initiation and propagation of short fatigue cracks in high-frequency mechanical impact (HFMI)-treated welded joints. The treated surface region, characterized by a compressive residual stress field, smooth notch geometry, and work hardening layer, improves welded joints’ fatigue strength. However, how these surface conditions influence the fatigue damage process zone during short crack initiation and growth is not yet well known. Therefore, this study systematically investigates the influence of different surface characteristics on fatigue life modeling of HFMI-treated welded joints made of high-strength steel. This is achieved using a non-local continuum damage mechanics-based approach of crack growth and elastic–plastic finite element simulation, explicitly modeling treated surface conditions. The simulated fatigue life is first verified with experiments and then applied to various surface conditions. The simulation results show that most of the fatigue life is spent until a crack size of 0.2 mm. The compressive residual stress field greatly extends both short crack initiation and propagation life, with its degree of contribution highly dependent on loading history and residual stress change. The role of the work hardening layer is mainly concentrated on improving fatigue life during short crack initiation and the very beginning of short crack growth.

Fatigue performance of Q420C high-strength steel at room and low temperatures

Steel structures are frequently exposed to variable-temperature environments, in which is it difficult to predict the fatigue failure of the steel. In this work, standard Q420C high-strength steel specimens were tested to explore their fatigue performance at room temperature (25°C) and low temperatures (0°C, −15°C and −30°C). Tensile tests were conducted before fatigue tests, and the results showed that the yield and ultimate strengths of Q420C steel increased significantly with a decrease in temperature. The fatigue behaviour of Q420C steel was assessed from different perspectives, including crack initiation, crack growth, fracture mode and fatigue life. Fatigue failure was observed mainly near the arc transition section of the specimen, with a fatigue crack initiating from the surface and internal discontinuity defects. Furthermore, the test fatigue life was compared with the recommended stress–fatigue life (S–N) curves from the specifications of various countries. These results suggest that the recommended S–N curves are excessively conservative for evaluating steel fatigue life at low temperature, leading to a potential economic cost for steel structures in extremely cold conditions. To avoid needless loss, a calculation method for steel fatigue life considering the effects of low temperature, stress range and yield strength was developed.

(Invited) Dry Electrode Technologies Toward High Energy Density and Low-Cost Lithium-Ion Battery

The electric vehicle (EV) market has grown very rapidly to meet the demand for net-zero carbon emissions in the transportation sector. The rapid growth of EVs is primarily attributed to the technological advances in lithium-ion batteries, making them the most promising energy storage devices due to their outstanding electrochemical performance. In recent years, the lithium-ion battery industry has made attempts to achieve price and driving range parity between electric vehicles and internal combustion vehicles. Significant efforts have been devoted to developing electrode processes as well as active materials in order to achieve low-cost and high-energy-density lithium-ion batteries. Particularly, the adoption of thick film electrodes is an effective way to increase both energy density and cost efficiency by reducing the amount of inactive materials, such as current collectors, separators, and cell components. In this presentation, we introduce the dry electrode technology to achieve ultra-thick film electrode. Dry electrode technology has the potential to provide a breakthrough in achieving higher loading levels and electrode densities. Moreover, the distribution of binders in dry electrodes does not impede lithium-ion transport, unlike wet electrode binders such as PVdF. Due to these synergistic effects, dry electrode-based electrodes have achieved ultra-high loading levels with lower resistance compared to wet-based electrodes. Additionally, dry electrode technology on the anode side has limitations due to the low low lowest unoccupied molecular orbital level (LUMO) level of the PTFE binder, resulting in side reaction during lithiation. This phenomenon significantly worsens battery performance, affecting factors such as initial Coulombic efficiency and cycle life. We suggest an effective strategy to mitigate the side reactions of dry-electrode technology.

Hydrodynamic Jet Cavitation to Process Natural Graphite into High C-Rate Capable Anodes for Use in Pouch Cells

A novel method for processing natural graphite for use in high performance Li-ion batteries is presented. The processing method utilises hydrodynamic jet cavitation (HJC) to produce a highly conductive graphite powder from a natural graphite precursor with the only consumables being electricity and water (process shown in Figure 1a). The HJC process produced a thin (carbon black)-like coating on the surface of the graphite particles, giving the material a higher conductivity compared to two other commercial graphite samples. In rate capability tests, LFP // graphite full cells produced a specific capacity 500% than the commercial graphite anodes (Figure 1c).This patented process is carbon neutral and aims to help the global electric vehicle (EV) market to produce high performing EVs whilst simultaneously lowering the high carbon footprint from producing the battery packs that power them.An in-depth characterisation study is performed on the powders, electrode slurry formulations and cells to determine how the surface characteristics of the graphite particles affect their electrochemical performance. The graphite powders were separated by particle size and tested in both coin and single layer pouch cells. Through SEM analysis, HJC graphite powders show a higher proportion of edge planes compared to basal planes, providing more sites for Li (de-)intercalation during charging and discharging (shown in Figure 1b). This explains their higher capacity at higher C-rates (5C + 10C) compared to the commercial standards. However, it is also found that the higher proportion of edge planes results in a substantially thicker solid electrolyte interphase (SEI) during cycling, consuming more of the Li inventory; resulting in a poorer initial coulombic efficiency and cycle life. The addition of electrolyte additives such as Lithium difluorooxalatoborate (LiDFOB), vinyl carbonate (VC) and VC derivatives are used to improve the coulombic efficiency of the coin and pouch cells. Figure 1

Ratcheting behaviour of Stellite 21 as laser cladding material for flange tip lift crossings repair

Laser cladding holds the promise to repair damaged rails, including flange tip lift crossings (FTLC) in tram rails. In order to further understand the effectiveness of laser cladding against rail damage, this study investigated the ratcheting behaviour of the laser cladding alloy Stellite 21, used in FTLC repairs, in comparison to the currently used rail steel grade R260. Experimental studies were conducted under uniaxial and biaxial stress-controlled cyclic loads. The study found that under identical uniaxial stress conditions, Stellite 21 exhibits superior ratcheting behaviour compared to R260 steel. Various mean stresses and stress amplitudes were also studied, revealing that increases in mean stresses or stress amplitudes resulted in higher ratcheting strains and ratcheting strain rates. Additionally, biaxial compression-torsion cyclic loading tests were performed on the R260 to replicate real-life stress conditions. The results indicated that the direction of plastic strain accumulation depended on the direction of the applied non-zero mean stress. The findings from this study are essential for calibration of parameters of cyclic plasticity models, which can be used to simulate ratcheting performance of laser-cladded FTLCs under in-service conditions for the prediction of fatigue crack initiation life and maintenance requirements of flange tip lift crossings.

Predicting fatigue crack initiation life in typical joints of offshore observation tower structures

ABSTRACT Tubular structures are widely used in steel constructions, such as offshore platforms, because of their superior mechanical qualities, efficient use of materials, lightweight and aesthetically pleasing appearance. The most common failure mode of offshore tubular joints is fatigue damage brought on by cyclic loading during the course of their service life, like wind, wave and equipment vibration. In this paper, the finite element model of the TK-type tubular joint at the stress concentration position is established by analyzing the load and response of the observation tower. The continuum damage mechanics method has been used to evaluate the fatigue crack initiation position and life of the tubular joint, and the crack initiation life of the key nodes has been predicted, which provides theoretical support for ensuring the service safety of the offshore observation tower.

Analysis of tooth root three-dimensional fatigue crack initiation, propagation, and fatigue life for spur gear transmission

The gears in aviation gear systems are susceptible to fatigue fracture due to high-speed, heavy-load, and load alternation operating conditions. Therefore, a numerical calculation model with multiple mesh positions loading form has been proposed in this paper to analyze the fatigue crack initiation and propagation behavior, and to estimate the fatigue life of these gears. The fatigue life of the gear is determined by separately calculating the fatigue crack initiation life and the fatigue crack propagation life. The tooth root fatigue stress and the fatigue initiation life are calculated by the multi-axial fatigue life prediction method with the Smith-Watson-Topper criterion and the critical plane method. Afterwards, the tooth root stress–strain field is calculated in Finite element (FE) software and the stress intensity factors of the crack tip are calculated in three-dimensional (3D) crack analysis software. Then, the tooth root fatigue crack propagation trajectory and the fatigue crack propagation life are obtained separately. Finally, the influence mechanism of the loading conditions, the geometry parameters of gears, and the initial crack positions on the tooth root fatigue crack initiation life, propagation life, and fatigue crack propagation trajectory are analyzed, and a tooth fatigue test bench is built for verifying the crack propagation trajectory.

Pore-based prediction of crack initiation life in very-high-cycle fatigue

The porosity of the material produced by additive manufacturing technology gives rise to a notable dispersion of the crack initiation life in the very-high-cycle fatigue regime. The crack initiation life in the very high cycle fatigue regime can be divided into the initial crack initiation life and early microcrack growth life. This paper proposed a model considering the effect of pore morphology and location to predict the initial crack initiation life. The average local stress in a grain near the pore is modified by considering the relationship between pore roundness, inclination, position, and stress concentration factor. The growth life of early microcrack is determined by integrating empirical formulas based on dislocation theory. Subsequently, the probability distribution of crack initiation life is obtained, which is in good agreement with the experimental results. The competition factor is proposed to quantitatively evaluate the tendency of crack initiation from the surface or the interior, taking into account the influence of local average stress and grain size. The predicted load corresponding to the shift in crack initiation position is in accordance with the experimental results.

Accumulated crystal plasticity dissipation energy driven continuum damage two-scale model for fretting fatigue initiation life

Accumulated crystal plasticity dissipation energy driven continuum damage two-scale model for fretting fatigue initiation life

Fatigue life assessment and verification of turbine joints: current status and prospects

The research status of fatigue life assessment technology for turbine joint structures is introduced. The progress, shortcomings and development trends of existing research are discussed from the aspects of multi-field load analysis, crack initiation life assessment, crack propagation simulation and test technology. The evaluation methods of service life and damage tolerance of turbine joint structures are discussed in detail. The results show that the existing analysis and test methods can basically realize the fatigue life assessment of turbine joints, but due to various limitations, the engineering applicability needs to be improved urgently. Robust load reduction analysis methods, life assessment methods based on physical mechanisms and data-driven, load history-related crack propagation life assessment methods and test technologies under complex thermal environments are still needed to establish a fatigue life assessment and verification system for advanced aero-engine turbine joint structures.

PROSPECTIVE RESERVE AND FULL PRELIMINARY TERM RESERVE ON ENDOWMENT LAST SURVIVOR LIFE INSURANCE USING CLAYTON COPULA

Combined life insurance is a type of insurance that protects two or more people who are related by family and is divided into two, namely joint-life life insurance and last-survivor life insurance. The last survivor life insurance is a condition of life insurance that will continue if there is at least one of all insurance participants who is still alive and will stop if all insurance participants die. The insurance company has to pay the benefit to the heirs of the insurance participant. When a claim occurs, the insurance company must prepare the reserve fee. The purpose of this research is to determine the amount of premium reserve of endowment last-survivor life insurance using prospective reserve and full preliminary term reserve. Full preliminary term reserve is one of the modified premium reserve calculations from Zillmer Reserve. To determine prospective reserve and full preliminary term reserve using the initial life annuity, single premium, and annual premium. Whereas the initial life annuity is influenced by the combined life and death opportunity of the insurance participants. Furthermore, the combined life and death opportunity of insurance participants will be obtained from Clayton copula and to obtain the parameter of Clayton copula, Rstudio software is used. Based on the result, the value of prospective reserves and full preliminary term reserves has increased every year and prospective reserves produce a greater value than full preliminary term reserves. If the insurance company uses this reserve calculation, the reserve that the company must prepare will increase every year. This is useful for insurance companies in predicting the amount of reserves they must have.

Impact of milk feeding regimens on growth, intake, efficiency, and costs in pre-weaned crossbred calves

The high milk (20% of weight) feeding in initial life is beneficial for growth, feed efficiency, and welfare of calves. The experiment aimed to evaluate the impact of different milk-feeding regimens on the growth, intake, physiological responses, blood and faeces attributes, feed efficiency, and feeding cost in crossbred calves. Thirty (n=30) healthy pre-weaned crossbred calves (75% HF × 25% Kankrej) were divided into five groups using a completely randomized design. The calves were fed milk 10% of body weight (T1); 4 L/day during the entire experiment (T2); 6,4,2 L/day during 2-6, 7-9, and 10-13 weeks of age (T3); and early weaning protocols 7, 5 L/day during 2-6, and 7-9 weeks of age (T4); as well as 8, 4 L/day during 2-6, and 7-9 weeks of age (T5), respectively after an adaptation of seven days. The feeding of concentrate, dry, and green fodder was common in all groups. The effect of milk-feeding regimens on body weight, body measurements, intake, and feed efficiency were non-significant. The evaluation of physiological responses, faecal consistency score, and blood haematology indicated that it was safe to feed different milk regimens. The milk feeding up to 13 weeks of age (T1, T2, T3) significantly lowered the cost of feeding for weight gain than the early weaning protocol (T4, T5). Among them, the feeding of T3 regimen was economical for weight gain without affecting the growth performance, feed efficiency, and health attributes of crossbred calves.

Surface fatigue characterization and its enhancement by the engineered ultrasonic rolling process for 300 M ultrahigh strength steel

The fatigue life of surface layer (FSL) is innovatively characterized to accurately capture the effect of surface integrity on the fatigue behavior of the components. The sensitivity of FSL of 300 M ultrahigh strength steel to the surface integrity indexes induced by representative manufacturing processes was analyzed by analytical modeling and fatigue tests from the perspective of engineering fracture mechanics. The ultrasonic surface rolling process (USRP) was introduced to optimize the fatigue limit of 300 M steel, and the improvement in fatigue life was experimentally quantified. Besides, the fracture analysis was conducted to provide the reason why USRP can enhance the fatigue behavior of 300 M steel. The results show that FSL occupies a majority with percentage of over 95 % in the entire fatigue life and a strong relation with the machined surface defects, especially the surface machining marks. The excellent surface finishing effect and high compressive residual stresses induced by engineered USRP could transfer the crack source from surface machining marks into subsurface inclusions, which greatly prolongs the fatigue crack initiation life and thereby the entire fatigue life. To be specific, the fatigue life was elevated by more than 40 times and the fatigue strength was increased by 34.7 % after USRP for the tested 300 M steel.

Numerical modelling for predicting corrosion initiation life of reinforced concrete square piles under reverse-seepage pressure

Numerical modelling for predicting corrosion initiation life of reinforced concrete square piles under reverse-seepage pressure