Life Curves Research Articles

Predicting Low Cycle Fatigue Life through Simulation of Crack in Cover Plate Welded Beam to Column Connections

This paper presents a low cycle fatigue life curve by simulating a crack in a cover plate welded moment connection. Initiation of ductile fracture in steel is controlled by growth and coalescence of micro-voids. This research used a numerical method using finite element modeling and simulation of ductile crack initiation by a micromechanical model. Therefore, a finite element model of a cover plate welded moment connection was developed in ABAQUS software, and a FORTRAN subroutine was used in order to simulate cracking in the connection model. Thus, each crack location and the number of cycles to initiate the crack were detected. Utilizing cyclic void micromechanical model of growth analysis, which is a technique to predict fracture in a ductile material, six different cover plate connections (divided in three categories) were modeled in the steel moment frame, and then their critical points to trigger the crack were identified. Finally, for the cover plate moment connection, considering the constant amplitude of loading curves data and in order to present the low cycle fatigue life prediction, displacement versus the number of half cycles diagram is produced.

Low-Cycle Fatigue Behavior of Al1070 Severely Deformed by Equal Channel Angular Pressing Process

In this paper, the low-cycle fatigue behavior of commercially pure aluminum severely deformed through equal channel angular pressing was studied by the use of data gathered from rotating-bending tests. After designing and manufacturing a suitable die, four passes of severe plastic deformation through strain path B c were successfully performed on aluminum samples. The annealed and processed samples were then subjected to simple tensile test, Vickers hardness test and rotating-bending fatigue test. The results showed a significant increase in the hardness and yield strength of processed samples but also a significant decrease in their ductility. A simple mathematical analysis was used to calculate the plastic strain applied in the fatigue test, and then the strain–life curves were plotted for the low-cycle region. The plotted strain–life curves showed that, as compared with annealing, the equal channel angular pressing process greatly reduces the transition fatigue life (N t) of commercially pure aluminum. Examination of Coffin–Manson curves obtained for samples subjected to annealing and severe plastic deformation revealed that equal channel angular pressing has an undesirable effect on the low-cycle fatigue of commercially pure aluminum and decreases the fatigue life in this region.

The prediction of multiaxial fatigue probabilistic stress–life curve by using fuzzy theory

AbstractThe fuzziness of the traditional multiaxial fatigue prediction model is discussed and the fuzzy theory is applied into fatigue reliability analysis. The fuzzy linear regression analysis method is used to determine the fuzzy coefficients in the multiaxial stress–life equation under a small sample condition, and the corresponding multiaxial fatigue probabilistic stress–life curve is calculated with different confidence levels.

Generalized definition of “crack-like” notches to finite life and SN curve transition from “crack-like” to “blunt notch” behavior

We start by generalizing the concept of “crack-like” notches to finite life. We note that, according to the well established Critical Distance Method (originally proposed by Neuber and Peterson), SN curves of all notches are very close to SN curves for cracked specimen, up to a certain number of cycles N∗, above which they tend to the SN curve of the uncracked/unnotched (plain) specimen, reduced by the stress concentration factor Kt. We suggest therefore new simple estimates for rapid assessment of the notch effect under finite life: for the “crack-like” notch, substituting the notch with a crack leads to immediate use of crack solutions in databases, whereas the knowledge of the stress ahead of a notch is also well known analytically in many cases, or can be adapted. We show one example with the SAE keyhole tests, leading to fully analytical SN curves, in much better agreement with experiment than, for example, strain-life approaches using Neuber’s rule.

Estimate of mortality reduction with implementation of advanced automatic collision notification

ABSTRACTObjective: Advanced Automatic Collision Notification (AACN) is a system on a motor vehicle that notifies a public safety answering point (PSAP), either directly or through a third party, that the vehicle has had a crash. AACN systems enable earlier notification of a motor vehicle crash and provide an injury prediction that can help dispatchers and first responders make better decisions about how and where to transport the patient, thus getting the patient to definitive care sooner. The purposes of the current research are to identify the target population that could benefit from AACN, and to develop a reasonable estimate range of potential lives saved with implementation of AACN within the vehicle fleet.Methods: Data from the Fatality Analysis Reporting System (FARS) years 2009–2015 and National Automotive Sampling System–Crashworthiness Data System (NASS-CDS) years 2000–2015 were obtained. FARS data were used to determine absolute estimates of the target population who may receive benefit from AACN. These estimates accounted for a number of factors, such as whether a fatal occupant had nearby access to a trauma center and also was correctly identified by the injury severity prediction algorithm as having a “high probability of severe injury.” NASS-CDS data were used to provide relative comparisons among subsets of the population. Specifically, relative survival rate ratios between occupants treated at trauma centers versus at non-trauma centers were determined using the nonparametric Kaplan–Meier estimator. Finally, the fatality reduction rate associated with trauma center care was combined with the previously published fatality reduction rate for faster notification time to develop a range for possible lives saved.Results: Two relevant target populations were identified. A larger subset of 6893 fatalities can benefit only from earlier notification associated with AACN. A smaller subgroup of between 1495 and 2330 fatalities can benefit from both earlier notification and change in treatment destination (i.e., non-trauma center to trauma center). A Kaplan–Meier life curve and a multiple proportional hazard model were used to predict the benefits associated with transport to a trauma center. The resulting range for potential lives saved annually was 360 to 721.Conclusions: This analysis provides the estimates of lives that could potentially be saved with full implementation of AACN and universal cell coverage availability. This represents a fatality reduction of approximately 1.6% to 3.3% per year, and more than double the lives saved by earlier notification alone. In conclusion, AACN is a postcrash technology with a promising potential for safety benefit. AACN is therefore a key component of integrated safety systems that aim to protect occupants across the entire crash spectrum.

On accelerated random vibration testing of product based on component acceleration RMS–life curve

Accelerated random vibration testing is usually used to certify a product in random vibration environments. The current certification method is based on the inverse power law and is strictly valid only for Basquin’s type of damage and fatigue of materials. Based on the response spectrum analysis of the product in “the simply scaled accelerated vibrations” and taking the size of acceleration power spectral densities (PSD) the component is undergoing as an index to characterize and compare the damage of the component in different experiments, this paper develops a more practical method in engineering for accelerated random vibration testing of the product in the framework of linear random vibration theory and the rule of acceleration root mean square (RMS)–life curve of the component. The suggested method shows that the time scale is determined by the zero-th and second-order response acceleration spectral moments of the component in real vibration and that simulated in the laboratory, which demonstrates its potential value and advantage in practical application when compared with that based on the von Mises equivalent stress. Simplifications of the method are discussed in detail. In “the simply scaled accelerated vibrations”, the time scale is determined by the acceleration root mean square of the component in real or simulated vibration. It is coincident with the form reported by Allegri but having different physical significance in the case of Basquin’s type of damage and fatigue of the component. The validation experiment with a desk computer was carried out, leading to the verification of the present method.

Effect of tensile dwell on high-temperature low-cycle fatigue and fracture behaviour of cast superalloy MAR-M247

Hot isostatically-pressed, nickel-based superalloy MAR-M247 was tested under fatigue and creep-fatigue conditions. Continuous cycling and cycling with 10min tensile dwells in each cycle were applied in symmetrical strain control cycle with constant total strain amplitude at 900°C in air. Cyclic hardening/softening curves, cyclic stress-strain curves and fatigue life curves were obtained. The introduction of tensile dwells resulted in lower fatigue life in total strain representation. Surface relief, specimen sections and fracture surface observations revealed crack initiation sites, crack density and crack paths, and help to clarify the effect of dwells on fatigue behaviour.

Fatigue Assessment of Explosive Bolts Considering Vibration of Fixtures

In order to comprehensively evaluate the safety and reliability of a missile, this paper gives a process of how to perform fatigue assessment for release devices—such as explosive bolts—considering road roughness during its carrying on different classes of roads. Firstly, displacement power spectral density (PSD) function is used to fit models of road surfaces of Class A, C, and E. Taking the surface models as simulations, multi-body dynamics analyses with code ADAMS are performed to obtain acceleration responses of different points on the missile. Loading these accelerations, the corresponding stress distribution of explosive bolts is achieved with FEM code ABAQUS. These loads are counted by rainflow method. Finally, constant life curves with different survival rates are employed to get the S-N curves at different stress ratios and stress concentration coefficients, and fatigue lives of explosive bolts are assessed based on the stress-life method. Afterward, the effect of pretension force on the vibration load is obtained. This paper provides a fatigue evaluation procedure for release devices, which is helpful to raise the reliability of release devices for both design and service procedures.

Fatigue Reliability Analysis of Wind Turbine Cast Components

The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting facilities and test facilities can affect the verification of properties by testing. Hence, it is important to have a tool to identify which foundry, cutting and/or test facility produces components which, based on the relevant uncertainties, have the largest expected fatigue life or, alternatively, have the largest reliability to be used for decision-making if additional cost considerations are added. In this paper, a statistical approach is presented based on statistical hypothesis testing and analysis of covariance (ANCOVA) which can be applied to compare different groups (manufacturers, suppliers, test facilities, etc.) and to quantify the relevant uncertainties using available fatigue tests. Illustrative results are presented as obtained by statistical analysis of a large set of fatigue data for casted test components typically used for wind turbines. Furthermore, the SN curves (fatigue life curves based on applied stress) for fatigue assessment are estimated based on the statistical analyses and by introduction of physical, model and statistical uncertainties used for the illustration of reliability assessment.

Rotating bending fatigue property of the Ni3Al-based single crystal superalloy IC6SX at 900°C

The high cycle fatigue behavior of a Ni3Al base single crystal superalloy IC6SX has been investigated at 900°C in this work. The specimens used for the fatigue tests were prepared by screw selection crystal method in a directional solidification furnace. The rotating bending fatigue tests were carried out at 900°Cin air, the stress ratio of R(σmax/σmin) was -1, and the rotating speed of the fatigue tests was 6500r/min(108Hz). The stress-fatigue cycle life (S-Nf) curve was obtained based on the fatigue tests, and the fracture surfaces were examined using scanning electron microscopy (SEM). It has been found that the median fatigue strength is 457.5MPa and the safety fatigue strength is 413.93MPa. And the fatigue fracture was composed of three different characteristic regions.

Residual Service Life Prediction for Bridges Based on Critical Life Curves

AbstractA residual service life prediction method based on critical life curves of selected bridge members is presented in this paper for bridges in service. The lowest target reliability index is ...

Application of hysteresis energy criterion in a microstructure-based model for fatigue crack initiation and evolution in austenitic stainless steel

The Sistaninia-Niffenegger Fatigue (SNF) model, a mesoscale hysteresis energy-based model of fatigue crack initiation, is calibrated and validated both by experiments and numerical modeling. The simulations are able to reproduce the fatigue life curves for the AISI 316L austenitic stainless steel of different grain sizes. In addition, it’s shown that the model captures the crack initiation site and the subsequent propagation through the anisotropic microstructure in a real multi-notched sample subjected to high cycle fatigue (HCF) loading. The microstructure of the polycrystal is determined by electron back scattering diffraction (EBSD), whereas the material properties of the polycrystal and the parameters of the model are obtained by inverse analysis using the Levenberg-Marquardt algorithm, based on the tensile stress-strain curves and the HCF test results, respectively. The model can be applied to different microstructures under HCF loading and evaluate crack initiation and its evolution with precision within the intrinsic scattering of HCF tests.

Effects of temperature and stress ratio on fatigue life of injection molded short carbon fiber-reinforced polyamide composite

The effects of temperature and stress ratio on fatigue life of short carbon fiber-reinforced polyamide-6 composite have been examined. Static tension and compression tests are carried out at room temperature (RT), 50°C and 70°C, respectively. For each of these temperatures, constant amplitude fatigue tests are performed at different stress ratios. Experimental results show that the temperature dependence of static strength can be described by a single equation of the Arrhenius type in the range higher than room temperature for each of tension and compression. The tensile strength turns to be smaller than the compressive strength at high temperature. The effect of temperature on fatigue life can approximately be removed by normalization of fatigue stress with respect to static strength, regardless of stress ratio. The asymmetry and nonlinearity in constant fatigue life diagram turns to be more significant with increasing temperature, and they can adequately be modeled by means of the anisomorphic constant fatigue life diagram. The temperature-dependent anisomorphic constant fatigue life diagram approach is also tested. It is demonstrated that this method allows adequately predicting the S-N curves for any stress ratios as well as the constant fatigue life curves for the whole range of mean stress at any temperature in a range that includes the test temperatures.

Comparative Analysis of Life Curve Mobile Application: an Easier Alternative to Existing Traditional Paper Partograph

Comparative Analysis of Life Curve Mobile Application: an Easier Alternative to Existing Traditional Paper Partograph

Low cycle fatigue life assessment of welded high-strength structural steels based on nominal and local design concepts

Fatigue life curves of butt joints, transverse stiffeners and sample components with tube-clevis connections, manufactured by active gas metal arc welding (GMAW) of S960QL, S960M and S1100QL high-strength steels, show a linear extension into the low cycle fatigue (LCF) regime with a constant slope up to the yield strength of the material. An extended S-N design curve based on fatigue class FAT 160 (k=5) gives conservative results for high quality butt welds below the ultimate tensile strength. In comparison to high frequency hammer peening and grinding, TIG dressing of S1100QL butt joints is most favorable for the increase of fatigue life.The effective notch stress approach with rref=1.00mm and measured radii of post treated welds leads to a reliable fatigue assessment up to at least N=5·103cycles to failure, which confirms FAT 225. The stress averaging approach using the microstructural support increases the assessment quality. A similar assessment reliability for damage parameter Wöhler lines, derived from elastic-plastic FE-analysis, is achieved, if support effects are considered.

Low and high‐cycle fatigue properties of an ultrahigh‐strength TRIP bainitic steel

AbstractThe scope of this study is to characterize the mechanical properties of a novel Transformation‐Induced Plasticity bainitic steel grade TBC700Y980T. For this purpose, tensile tests are carried out with loading direction 0, 45 and 90° with respect to the L rolling direction. Yield stress is found to be higher than 700 MPa, ultimate tensile strength larger than 1050 MPa and total elongation higher than 15%. Low‐cycle fatigue (LCF) tests are carried out under fully reverse axial strain exploring fatigue lives comprised between 102 and 105 fatigue cycles. The data are used to determine the parameters of the Coffin–Manson as well as the cyclic stress–strain curve. No significant stress‐induced austenite transformation is detected. The high‐cycle fatigue (HCF) behaviour is investigated through load controlled axial tests exploring fatigue tests up to 5 × 106 fatigue cycles at two loading ratios, namely R = −1 and R = 0. At fatigue lives longer than 2 × 105 cycles, the strain life curve determined from LCF tests tends to greatly underestimate the HCF resistance of the material. Apparently, the HCF behaviour of this material cannot be extrapolated from LCF tests, as different damage, cyclic hardening mechanisms and microstructural conditions are involved. In particular, in the HCF regime, the predominant damage mechanism is nucleation of fatigue cracks in the vicinity of oxide inclusions, whereby mean value and scatter in fatigue limit are directly correlated to the dimension of these inclusions.

A new, direct approach toward modeling thermo-coupled fatigue failure behavior of metals and alloys

The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and alloys over the whole deformation range up to failure. As contrasted with the usual elastoplasticity models, such new models of much simpler structure are totally free, in the sense that both the yield condition and the loading–unloading conditions need not be introduced as extrinsic coercive conditions but are automatically incorporated as inherent constitutive features into the models. Furthermore, the new models are shown to be thermodynamically consistent, in a further sense that both the specific entropy function and the Helmholtz free energy function may be presented in explicit forms, such that the thermodynamic restriction stipulated by Clausius–Duhem inequality for the intrinsic dissipation may be identically satisfied. Secondly, it is then demonstrated that the thermo-coupled fatigue failure behavior under combined cyclic changes of stress and temperature may be derived as direct consequences from the new models. This novel result implies that the new model can directly characterize the thermo-coupled fatigue failure behavior of metals and alloys, without involving any usual damage-like variables as well as any ad hoc additional criteria for failure. In particular, numerical examples show that, under cyclic changes of temperature, the fatigue characteristic curve of fatigue life versus temperature amplitude may be obtained for the first time from model prediction both in the absence and in the presence of stress. Results are in agreement with the salient features of metal fatigue failure.

Truncated Hybrid Double Acceptance Sampling Plan (THDASP) for Weibull Product Life Distribution

In this paper, an improved reliable acceptance sampling plan (Truncated hybrid Double Acceptance Sampling Plan (THDASP)) is proposed for products life that follows Weibull distribution when the testing is truncated at a specified time (t). This type of inspection sampling plan can be used to save the testing time in practical situations. The optimal sample sizes (n) required for testing product quality to ascertain a true mean life is obtained under a given Maximum Allowable Percent Defective (β), test termination ratios and acceptance numbers(C). The operating characteristic (OC) values formula is being developed considering both the Producer’s and Consumer’s risk and the values are generated. The Mean Life Ratios and curves of the plan are examined with varying ratio of the true mean life to the specified life. The advantage of this inspection plan is that could it results in better economic reliability product quality testing that protects the producer from rejecting his good lots and consumers from accepting bad lots of finished products. The mean life ratio values will also guides the producer on how to improve on his product’s quality. A numerical example is also discussed for illustrative purpose.

甘肃省民勤连古城自然保护区沙木蓼种群的结构与动态

PDF HTML阅读 XML下载 导出引用 引用提醒 甘肃省民勤连古城自然保护区沙木蓼种群的结构与动态 DOI: 10.5846/stxb201409281913 作者: 作者单位: 甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃民勤荒漠草地生态系统国家野外科学观测研究站,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省连古城国家级自然保护区管理局,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省荒漠化与风沙灾害防治国家重点实验室,甘肃省荒漠化与风沙灾害防治国家重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 甘肃省创新群体资助项目（145RJIA335）；甘肃省创新团队资助项目（1207TTCA002） Structure and dynamics of Atraphaxis bracteata populations in Minqin Liangucheng Nature Reserve, Gansu Author: Affiliation: State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,Gansu Minqin National Field Observation and Research Station on Ecosystem of Desertification Rangeland,Minqin,Gansu,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,,,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu,State Key Laboratory of Desertification and Aeolian Sand Disaster Combating,Wuwei,Gansu Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:根据甘肃省民勤连古城自然保护区沙木蓼种群的生境和植被差异，分别选择低山剥蚀残丘覆沙地（生境Ⅰ）和山前倾斜洪积扇沙地，有小型风积沙丘（生境Ⅱ）和无风积沙丘（生境Ⅲ）3种生境类型样地，对其种群的发育状况、年龄结构、静态生命曲线与分布格局进行了研究，揭示沙木蓼种群动态规律并评价其在构建荒漠植被方面的价值，为科学合理地管护和持续利用沙木蓼种质资源提供科学依据。研究结果表明，1）沙木蓼苗龄级、幼龄级、成熟龄级和老龄级种群密度大小顺序为生境Ⅲ > 生境Ⅰ > 生境Ⅱ，而3种生境中同龄级种群在株高、冠幅、新梢生长量方面差异不显著；2）苗龄级种群在3种生境下都占据了较大的优势地位，对沙木蓼种群的更新具有积极作用。生境Ⅰ和Ⅲ的幼龄级和成熟龄级的年龄结构为连续增长型，老龄级为独立的增长型，种群具有较大的发展空间。而生境Ⅱ的幼龄级和成熟龄级种群的年龄结构为连续的稳定型，老龄级种群为稳定型，种群结构比较稳定。3）种群lx，dx和qx曲线在苗龄级、幼龄级和成熟龄级阶段具有相同的变化趋势，其中苗龄级种群向幼龄级种群转变过程中均呈下降趋势，幼龄级和成熟级种群发育过程中基本保持平稳，但在老龄级种群阶段3种曲线变化趋势的差异性较大，其中生境Ⅰ和Ⅲ种群产生重叠，沙木蓼种群的死亡高峰主要发生在苗龄级和老龄级阶段，具有前期增长，中期稳定，后期衰退的一般规律。4）沙木蓼苗龄级、幼龄级和成熟级种群的分布格局均为聚集分布，而老龄级种群为随机分布。以上分析表明，3种生境下沙木蓼种群更新能力旺盛，种群结构趋于合理，生境差异（风沙流活动）只对土壤种子库、种子萌发和幼苗保存具有显著影响，对其它龄级种群发育没有显著影响，在荒漠植被演变中表现出较强的适应能力和优越性，因此沙木蓼在荒漠植被恢复和重建中具有重要的利用价值。 Abstract:The Minqin Liangucheng Nature Reserve has different types of habitats and vegetations of Atraphaxis bracteata populations. In this study, three types of habitats, i.e., the low denuded hills covered by gravel (habitat I), tilted alluvial fans with small aeolian sand dunes (habitat Ⅱ), and tilted alluvial fans without aeolian sand dunes (habitat Ⅲ), were selected to compare the development status, age structure, static life curve, and distribution pattern of A. bracteata populations at this reserve to reveal their succession dynamics, assess their ecological value, and provide the scientific knowledge for their rational management and sustainable usage. We found that (1) the population densities of young, mature, and old seedlings of A. bracteata were the highest at habitat I, followed by those at habitats Ⅱ and Ⅲ. However, there were no significant differences in the average height, average crown width, and new shoot growth among the same age groups at the three population habitats. (2) The seedlings of all ages dominated position at the three habitats and played a vital role on the propagation of A. bracteata. The age structures of young and mature populations at habitats I and Ⅲ showed continuous growth curves, but that of the old population showed a single growth curve, suggesting that A. bracteata populations at these habitats were developing. The age structures of young and mature populations at habitat Ⅱ showed continuous stable growth curves, but that of old population showed a single stable curve, indicating that A. bracteata populations at this habitat were stable. (3) The lx, dx, and qx curves of seedlings and young and mature populations at the three habitats showed similar change trends. These curves showed decreasing trends from seedling age stage to young age stage, and then stabilized in the young and mature age stages, whereas the curves of old age grade were significantly different, and the populations overlapped between habitats Ⅲ and I. This suggested that seedlings and older A. bracteata populations showed peak mortality, and there was a general pattern of growth at the earlier stage, which stabilized at the middle stage and then decreased at the later stage. (4) The distribution patterns of seedlings and young and mature populations were clump, whereas those for old populations were Poisson. The results indicated that the A. bracteata populations at the three habitats propagated vigorously and showed relatively optimal structure. The environmental difference among the three habitats only had significant impacts on soil seed bank, seed germination, and seedling preservation, but not on population development. These findings suggested that A. bracteata has strong adaptability and dominance in desert areas and can be restored and reconstructed. 参考文献 相似文献 引证文献

Resources industrialization channels and strategies of active polysaccharide from Lycii Fructus based on analysis of domestic and foreign intellectual properties

Lycii Fructus is a traditional medicinal and edible herb, with the function of liver and kidney nourishing, blood and eyesight replenishing. As the most important active substance in the fruits of Lycium barbarum, Lycium barbarum polysaccharides (LBP) have been demonstrated to play multiple pharmacological activities, with broad prospects for development and utilization. Based on the comprehensive deep analysis of global LBP patent output, the current patent LBP features were explored from the perspective of development trend, technology field distribution, time dimension, technology life curve and patent applicant. The development trend of Chinese LBP industry was also revealed. At present, the research and development of LBP is in the "development period", with a good development track in which the main research institutions remain domestic ones. At the same time, problem still presents in the lack of industrialization, which means that the advantage of natural resources has not been transformed into industrial advantages of LBP. The format of potential product group and prospect of LBP were also analyzed to provide scientific information for the effective development,comprehensive utilization and collaborative innovation mechanism of Chinese Lycium barbarum resources and LBP.