Fatigue Damage In Materials Research Articles

Numerical Approximation of Stochastic Systems for Composite Materials Based on Markov Chains

The crack density and crack growth rate are important parameters which are used to describe the fatigue damage and predict fatigue life of a composite material. Even the same good manufacturing practice, the fatigue damage of materials may be different. Also material properties often accompany random fluctuation. Thus stochastic systems are used to present the crack density and crack growth rate. It is surprising that there are not any numerical schemes established for hybrid stochastic systems in composite materials. In this paper, based on Markov chains, the Euler-aruyama method is developed, and the main aim is to show the convergence of the numerical solutions under the non-Lipschitz condition for hybrid stochastic material systems.

Establish Fatigue Life Mechanism for Self Run Bushing By Engineering Analysis Methods

Along with social progress, people pay attention to health. Modern people choose the gym to maintain posture and body functions well, therefore, the gym popularize everywhere. Popularity of expensive fitness equipment to bring a lot of convenience, but different users share of fitness equipment have different condition, often caused damage by use, which is the most important factor for the material fatigue damage. This study chose the exercise bike parts “self run bushing” to create a fatigue life assessment mechanism. In this study, to the fatigue analysis was conducted, by using finite element analysis according to the material S-N curve and Miner cumulative damage theory in a series of cyclic loading. To analyze fatigue life, analytical and experimental studies through mutual verification were conducted which can obtain the expectation life period of the self run bushing. The load spectrum based on different user can also be considered in this study. Based on the design frequency from different users, after the study of distribution of reliability and failure, the most appropriate time-out and the best replacement time can be obtained.

Comparison of Two Probabilistic Fatigue Damage Assessment Approaches Using Prognostic Performance Metrics

In this paper, two probabilistic prognosis updating schemes are compared. One is based on the classical Bayesian approach and the other is based on newly developed maximum relative entropy (MRE) approach. The algorithm performance of the two models is evaluated using a set of recently developed prognostics-based metrics. Various uncertainties from measurements, modeling, and parameter estimations are integrated into the prognosis framework as random input variables for fatigue damage of materials. Measures of response variables are then used to update the statistical distributions of random variables and the prognosis results are updated using posterior distributions. Markov Chain Monte Carlo (MCMC) technique is employed to provide the posterior samples for model updating in the framework. Experimental data are used to demonstrate the operation of the proposed probabilistic prognosis methodology. A set of prognostics-based metrics are employed to quantitatively evaluate the prognosis performance and compare the proposed entropy method with the classical Bayesian updating algorithm. In particular, model accuracy, precision, robustness and convergence are rigorously evaluated in addition to the qualitative visual comparison. Following this, potential development and improvement for the prognostics-based metrics are discussed in detail.

Repairing Surface Fatigue Damage of the Metal Material by Heat Treatment

In this paper, using experimental method studied to repair surface fatigue damage of the metal material by heat treatment. Analyzed the mechanism to repair surface fatigue damage of the metal material by heat treatment. From the test, it have been found that the Metal materials has temping threshold behavior in repairing it’s fatigue damage by heat treatment. For the same kind of material, there is a threshold characteristics in choosing tempering temperatures when repaired the fatigue damage of metal material surface through changed tempering temperatures. Experimental results shows that the temping temperature threshold to repair metal material fatigue damage is the first tempering temperature after materials was hardened before it was in fatigue damage.

Non-destructive evaluation techniques for assessment of creep and fatigue damage in materials and components

In this article, application of various non-destructive evaluation (NDE) techniques for assessment of creep and fatigue damage in materials and components has been discussed. X-ray diffraction technique has been used for finding fabrication-induced residual stresses in components. Ultrasonic and magnetic techniques have been applied for characterizing changes in microstructures due to creep and fatigue. Crack closure phenomenon and fatigue crack growth have been studied in austenitic stainless steels using acoustic emission technique. Dual-frequency eddy current technique has been used for high sensitive detection of fatigue cracks in compressor discs of aeroengines.

Evaluation of fatigue damage in materials using indentation testing and infrared thermography

Damage identification due to fatigue has been studied on 304-Stainless Steel and Al-Cu-Mg alloys 2014-T651 and 7175-T7351, using two different experimental methods: a) cyclic indentation, and b) infrared thermography. Indentation response during load controlled cyclic loading is used to characterize fatigue response of materials. The load vs. depth of penetration data obtained continuously during fatigue testing is used to obtain information on cyclic stress-strain behavior and onset of failure. Infrared thermography is used to study the heat generation during fatigue loading on specimens. The variables that affect the process are: frequency of loading, magnitude of strain (elastic-plastic), thermal properties. The temperature curve can be considered to be having three regions, initial region of rapid increase in temperature, followed by stable temperature rise and final rapid heat generation prior to failure. The slopes in the initial region and stable region are independent of prior damage history in materials in case of specimens subjected to pure elastic load reversals. In case of elastic-plastic loadings, the rate at which the temperature rises in initial region changes as a function of fatigue damage and can thus be used to estimate prior damage in materials.

Numerical investigations on the fatigue failure of forging tools due to thermo-mechanical cyclic loading

During service hot forging dies are exposed to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent cause of failure. Fatigue cracks in forging dies are caused by local elasto-plastic strains due to cyclic mechanical and thermal loads. Aiming at a reduction of tool and production costs of forgings, tool life extension is necessary. In order to reach this goal, process design and process optimisation are currently done with the help of the finite element analysis (FEA). An integral part of this procedure is the tool design based upon fatigue life maximisation of forging dies in the Low-Cycle-Fatigue (LCF) region. Within the framework of this research the material fatigue damage of a forging die due to cyclic thermo-mechanical loads is analysed based on FEA process simulations. Besides this a material model which considers cyclic elasto-plastic material behaviour was used to describe the constitutive behaviour of the forging dies. The results of a fatigue life damage analysis applied to an industrial forging process in which the lower die shows a clear fatigue crack initiation. The crack initiation sites predicted with the FEA process simulations agree with the ones observed on the real die component.

Effects of mechanical properties of concrete constituents including active mineral admixtures on fatigue behaviours of high performance concrete

ABSTRACTIn order to explore the links between the macroscopic and microstructural characteristics of concrete with admixtures of active mineral additions, four series of concrete prisms, of mortar matrix prisms and mortar‐aggregate Interfacial Transition Zone (ITZ) are prepared and tested under monotonic and cyclic loads. Five static mechanical parameters (compressive and bending strength, fracture energy, elastic modulus, Poisson ratio) and bending fatigue performance (fatigue life, critical maximum displacement and strain, fatigue damage) of such materials are experimentally evaluated. The results show that degradation laws of concrete properties under both monotonic and cyclic loads vary with the different cohesive strength ratio and elastic modulus ratio of ITZ and mortar matrix. The single or double additions of ground slag and fly ash with optimized mass fractions remarkably enhance the static and bending fatigue properties as well as change the failure mechanisms of concrete.

Computational modeling of mixed-mode fatigue crack growth using extended finite element methods

The extended finite element method (XFEM) combined with a cyclic cohesive zone model (CCZM) is discussed and implemented for analysis of fatigue crack propagation under mixed-mode loading conditions. Fatigue damage in elastic-plastic materials is described by a damage evolution equation in the cohesive zone model. Both the computational implementation and the CCZM are investigated based on the modified boundary layer formulation under mixed-mode loading conditions. Computational results confirm that the maximum principal stress criterion gives accurate predictions of crack direction in comparison with known experiments. Further popular multi-axial fatigue criteria are compared and discussed. Computations show that the Findley criterion agrees with tensile stress dominant failure and deviates from experiments for shear failure. Furthermore, the crack propagation rate under mixed mode loading has been investigated systematically. It is confirmed that the CCZM can agree with experiments.

Stress-Amplitude-Dependent Deformation Characteristics and Microstructures of Cyclically Stressed Ultrafine-Grained Copper

Various mechanical behaviors of ultrafine-grained (UFG) materials produced by equal channel angular pressing (ECAP) generally exhibit distinctive characteristics from those of conventional grained materials, so that the relevant studies have received sustained attention in recent years. Apparently, the understanding of the fatigue properties (among various mechanical properties) of such UFG materials is of particular importance for their practical engineering applications, many investigators have thus been attempting to explore the fatigue deformation mechanisms of UFG materials, especially of UFG copper, with different emphases. It is now commonly recognized that the low-cycle fatigue damage in UFG materials primarily results from the formation of shear bands (SBs), which can extend over far larger scales than the initial grain size, and that the cyclic softening phenomenon as well as the deterioration in fatigue life under strain-amplitude-controlled tests in the low-cycle fatigue (LCF) regime is attributed to grain coarsening due to instabilities of the ECAPed structures during cycling. On the contrary, the fatigue life of UFG materials obtained under stress-controlled tests in the highcycle fatigue (HCF) regime is normally enhanced greatly as compared to their conventional counterparts. However, the details about cyclic deformation microstructures and shear band features in LCF and HCF regimes, respectively, are less understood so far. To further understand the possibly different fatigue deformation mechanisms of UFG copper in LCF and HCF regimes, the present contribution is to report the effect of the applied stress amplitude on the cyclic stress response behavior, surface damage features as well as relevant microstructural changes of such UFG copper materials. The applied stress amplitudes ranging from 100 MPa to 200 MPa are adopted to ensure that fatigue tests are carried out within both LCF and HCF regimes.

Evaluation and prediction of fatigue resistance of metals from the kinetics of variation in surface properties

The paper studies the fatigue resistance of metallic samples subjected to high-cycle loading and microhardness measurement. The fatigue damage of materials during loading is identified as decrease in the thickness of the barrier surface layer, which prevents fatigue failure. It is shown that the thickness of this layer is independent of the plastic characteristics of the material and the level of stress. A method to evaluate accumulated fatigue damage is developed. Kinetic curves of damage accumulation are analyzed. Methods to predict fatigue characteristics are proposed

Simulation of near-tip crack behaviour and its correlation to fatigue crack growth with a modified strip-yield model

A modified strip-yield model has been developed to simulate the plasticity-induced crack closure under the constant amplitude (CA) and a single overload loading conditions. The paper focuses on the simulation of the near tip crack profiles and stress distributions during the fatigue process. Detailed information on near-tip stress and displacement fields at the maximum load (Pmax), the minimum load (Pmin), and the crack opening load (Pop) of a fatigue load cycle have been presented. The correlation of the crack closure to the near-tip material fatigue damage has been investigated and used to rationalise the crack growth behaviour under the CA and a single overload loading conditions.

Prognosis of Blade Material Fatigue Using Elman Neural Networks

Prognosis of major components such as blades, rotors, valves of steam turbine is crucial to reducing operating and maintenance costs. Prognostic strategies can assist to detect, classify and predict developing faults, guarantee reliable, efficient and continuous operation of electric plants, and may even result in saving lives. In this paper, a recurrent neural network based strategy was developed for blade material degradation assessment and fatigue damage propagation prediction. Two Elman Neural Networks were developed for fatigue severity assessment and trend prediction correspondingly. The performance of the proposed prognostic methodology was evaluated by using blade material fatigue data collected from a material testing system. The prognostic method is found to be a reliable and robust material fatigue predictor.

On-line damage detection on a wing panel using transmission of multisine ultrasonic waves

Fatigue damage of materials is an important problem that causes a lot of failures in mechanical systems. It is very important to detect this fatigue as early as possible. Nowadays, most of the nondestructive testing methods are off-line: the inspection is carried out periodically and in some cases the device has to be dismounted. So we risk to exceed, for example, the critical length of a crack. In this article, an on-line method based on the variation in transmission of a multisine ultrasonic wave during opening and closing of a surface crack is developed. As a validation experiment, a propagation fatigue crack in a sinusoidally loaded wing panel is considered. It will be shown that the on-line method is very sensitive to crack propagation.

Fatigue Crack Initiation in Crystalline Materials – Experimental Evidence and Models

Recent observations relevant to the early stages of the fatigue damage of crystalline materials are reviewed. Experimental evidence on the localization of the cyclic plastic strain and on the surface relief formation in cyclic loading of 316L austenitic stainless steel is presented. The focused ion beam is used for exposing three-dimensional evidence of persistent slip markings (PSMs). PSMs consist of extrusions and parallel or alternating intrusions which develop during cyclic loading. Monte Carlo simulations of vacancy generation within persistent slip band (PSB) and their migration to the matrix where they annihilate on the edge dislocations are used to simulate the growth of extrusions and intrusions. The results of the simulations are compared with experimental data and discussed in terms vacancy models of fatigue crack initiation.

Information models of self-organization and fatigue damage of metallic materials

Information models of self-organization and fatigue damage of metallic materials

Mechanisms and kinetics of the early fatigue damage in crystalline materials

The localization of the cyclic plastic strain and its effect on the hysteresis loop, on the surface relief evolution and on the internal dislocation structure of austenitic and ferritic stainless steels are presented. Extrusion and intrusion formation is studied using atomic-force microscopy. The experimental findings concerning the surface relief formation and crack evolution are confronted with existing models of fatigue-crack initiation. Short crack growth kinetics is documented and the short crack growth law and its parameters are compared with the Coffin–Manson law.

Study on Evaluation of Fatigue Damage of MIM Materials with AE Method (1st Report, Application of Chaos and Frequency Analysis)

Study on Evaluation of Fatigue Damage of MIM Materials with AE Method (1st Report, Application of Chaos and Frequency Analysis)

Mechanisms of the Early Fatigue Damage in Metallic Materials

The early stages of the fatigue damage in f.c.c. and b.c.c. metals are studied using high resolution techniques. The localization of the cyclic plastic strain results in formation persistent slip bands (PSBs) with specific dislocation structure. Characteristic surface relief is formed at locations where PSBs emerge on the surface. It consists of extrusions and intrusions separated by the original flat surface. Atomic force microscopy is used to study the details of the surface relief. The experimental findings are discussed in terms of the point defect model of fatigue crack initiation.

Frontiers in NDE research nearing maturity for exploitation to ensure structural integrity of pressure retaining components

In this paper, research and developmental efforts that demonstrate high sensitivity detection and characterization of defects and assessment of microstructural degradation, residual stresses and fatigue damage in materials using different non-destructive evaluation (NDE) techniques, have been discussed. Applications of eddy current techniques for quantitative defect characterization and for generalized applications, and remote field eddy current technique for inspection of steam generator and heat exchanger tubes have been discussed. Advanced ultrasonic methods such as time of flight diffraction, synthetic aperture focusing technique, phased array and signal processing for detection, characterization and imaging of defects have been discussed. Applications of ultrasonics and magnetic Barkhausen emission techniques for characterization of microstructures and residual stresses have been discussed. Applications of acoustic emission and infrared thermography techniques for weld quality evaluation of critical nuclear components as part of intelligent processing of materials (IPM) work have been discussed. Application of acoustic emission technique for integrity assessment of pressurized components has been discussed. Development of a software called assets and infrastructure management system (AIMS), for storing and retrieving information for various materials, components and systems, has also been highlighted. The techniques and applications discussed are result of systematic and innovative R&D efforts in the multidisciplinary areas of physics, materials, instrumentation, sensors and softwares for providing solutions to various challenging problems.