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In this study, a new method of replaceable supporting member within orthotropic steel box girder is proposed in order to reduce stress amplitude and improve fatigue life of orthotropic steel box girder. The component model was established by ABAQUS, and the experiment was conducted to analyze stress amplitude of easily fatigue cracking areas of orthotropic steel box girder with and without the supporting member. In addition, the fatigue life was analyzed and predicted. The comparison results show that the finite element analytical results are in good agreement with the experimental results. The reduced proportion of stress amplitude of U rib, T rib grooves and mid-span of top plate of orthotropic steel box girder range from 40% to 60% and 20% to 40%, respectively. The analytical results show that the stress amplitude of orthotropic steel box girder can be reduced by the similar extent with the addition of the same supporting member under different loading pressure; The supporting member can improve the fatigue life of orthotropic steel box girder pertinently, which is simple in construction and low in cost, and can provide suggestions for solving fatigue problem of orthotropic steel box girder in engineering practice.

In this contribution, it was suggested an extension of Gurson model for cyclic application, regarding the prediction of fretting fatigue life and the study of the influence of the plastic strain field on fretting fatigue for an aluminum alloy 7050-T7451. In this setting, a modification in the defects growth mechanism was done, including a variable that distinguishes the evolution rate of Gurson damage in tension-compressive loads and, the coupling of the Xue shear mechanism to the extension of the model to low range of stress triaxiality. Initial simulations were performed for traditional fatigue tests and the suggested model has worked in good agreement with experimental data. After that, experimental fretting fatigue tests were proposed and carried out in order to observe the influence of the contact pressure of the fretting pad on the fretting specimen and in the system life. Numerical simulations were performed, considering now the modeling of the fretting fatigue problem by Finite Elements Method and life predictions were calculated, applying the suggested Gurson-based continuum damage formulation, by an analysis in a Gauss point. The calculated and observed life diagram has shown a robustness performance of formulation, predicting lives within a band factor of 2. It was also verified that the plastic strain field introduced, due to the increase in contact pressure on the fretting pad, benefits the specimen life, since the plastic strain was induced by the appearance of dislocations, which causes a hardening and an increase of the macroscopic material properties, as well as a negative mean stress into the specimen.

Fatigue cracking of rib-to-deck welded joints is the major fatigue problem of the orthotropic steel deck (OSD). It is important to evaluate the fatigue performance improvement of rib-to-deck double-side welded joints in an OSD when compared with single-side welded joints. In this study, the software ABAQUS and FRANC3D were used to set up a multiscale finite element model for segments of an OSD. Under vehicle load, the mode I stress intensity factor (SIF) of a fatigue crack at the rib-to-deck single-side and double-side welded details without or with the effect of welding residual stress was computed. The relationship between the mode I SIF of the fatigue crack and the key parameters was analyzed, including welded penetration, thickness of deck plate and the initial crack surface length and depth. The results showed that the welding residual stress can significantly influence the SIF values of the rib-to-deck welded joints in the OSD. The maximum SIF of the crack in the rib-to-deck double-side welded joints was 29.6% less than that of the single-side welded joints, which can effectively improve the fatigue performance of the rib-to-deck welded joints. The effect of the welded penetration rate on the fatigue performance of rib-to-deck double-side welded joints was only slight. By increasing the thickness of the deck, reducing the initial crack surface length and depth, the SIF of cracks in the rib-to-deck double-side welded joints can be significantly decreased, and this approach improves fatigue performance.

For warships with long superstructure and complex cabin structure, the obvious stress concentration at the superstructure end had generally led to serious fatigue problem.

Sustained loads have for some Ni-based superalloys been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on the interaction of load cycles, overloads, and temperature. However, vibrations of different kinds are to some extent always present in engine components, and an investigation of how such loads affect the dwell time cracking, and how to incorporate them in a modelling context, is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical crack propagation testing has been conducted at 550 °C for surface cracks with and without the interaction of superimposed vibrational loads. Subsequent investigation of the fracture behaviour was performed by scanning electron microscopy and the modelling work has been conducted by incorporating the vibration load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical test results. Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

The study of near-threshold fatigue crack growth has long remained an empirical field due principally to the highly microstructure-sensitive nature thereof. The primary challenges have been to forward physical model(s) informed by the governing micromechanism(s), which would be able to predict the experimental behaviors devoid of empiricism. Today, we have sophisticated experimental techniques (e.g. digital image correlation, electron microscopy) as well as atomistic simulation tools (e.g. molecular dynamics) at our disposal to finally revisit the century old fatigue problem in the light of physical phenomena therein. This paper is geared towards achieving such a feat with a very special type of materials, nano-twinned alloys, as the candidate materials, which are of great recent interest due to their reportedly superior damage properties. Specifically, we investigate how the microstructural features (e.g. slip transfer mechanism at coherent twin boundaries, twin thickness/spacing, frictional stress, pre-existent near-tip slip density) can be modulated to improve the damage resistance. The results suggest that these parameters considerably affect the crack propagation impedance (as quantified in terms of Δ K eff th ). A thorough discussion of the current findings and the most recent literature developments in this regard are provided.

As the general features of fretting fatigue, initiation of fretting fatigue crack is in the very early stage of the fretting fatigue life and there are small non-propagating cracks in the test specimen that doesn't fracture at the fretting fatigue limit. In accordance with these experimental facts, fretting fatigue problem can be considered as a propagation problem of small crack. Thus, a pre-cracked specimen was used in the fretting fatigue test in this study. The objective was to consider the determinant factors of fretting fatigue strength. In the fretting fatigue test, the fretting fatigue limit of the pre-cracked specimen was once reduced and after increased with increase of the contact pressure. The reason was understood by the stress intensity factor of the pre-crack obtained by a finite element analysis. In this study, the fretting fatigue limit can be predicted by the comparison of ΔK of the pre-crack and the propagation threshold of the pre-crack ΔKth. The effect of the relative location of the pre-crack to the contact edge on the fretting fatigue strength was also discussed by both fretting fatigue test and FEM analysis.

Attention has been focused on the fatigue problem for compacted graphite iron, when detonation pressure and temperature becomes higher and higher in combustion chamber for a long time. The compacted graphite iron plays an important role in the cylinder head of diesel industry for its good combination of thermal and mechanical properties. The damage mechanisms of compacted graphite iron under fatigue loading are observed in this study by scanning electron microscope (SEM) and in situ technique at elevated temperatures. The results show that tensile strength of compacted graphite iron decreases slightly at first, then decreases dramatically with the increasing temperature, which is a common phenomenon, even of various metallic materials. For the compacted graphite iron, these two stages are mainly controlled by different transformation mechanisms: the former mechanism, slip band stage, is affected by the inhibition of dislocation movement including strain strengthening, dynamic strain aging and precipitation hardening; and the latter, boundary sliding stage, is controlled by the vacancy diffusion. The newly proposed mechanisms can provide a new clue for the optimization of cast iron design. These damage mechanisms lay the foundation for the application of the crack technology.

Many mechanical components are subjected to multiaxial fatigue. These conditions are typically coming from external loads, the geometry of the component and/or residual stresses. However the majority of experimental data available in the literature are focused on the simpler uni-axial fatigue problem. The present work describes a series of experimental tests conducted to characterise in a comprehensive way the multiaxial behaviour of a ST52-3N structural steel. First, the monotonic properties of the steel were obtained experimentally. Then cyclic properties were also measured both in the longitudinal and torsional axes. Finally another series of tests were carried out to study the multiaxial response of the material. Both in-phase (proportional) and out-of-phase (non proportional) loadings were employed, thus providing a complete database for improving current models which describe the multiaxial behaviour of materials.

The present paper aims at studying a high-pressure hydrogen storage vessel, combining a steel liner and a wrapped composite reinforcement. Nowadays, this means of storage is notably used in transport. However, limits appear insofar as fatigue problem happens when the operating pressure is 700 bar. This matter has to be solved. This study tries to arrange a method to build a 700 bar vessel which could resist to cyclic pressure loading, and particularly focuses on the behaviour of the liner which seems to be the critical element to control. In addition, as a large part of this gaseous storage is bound to be on board, the composite optimization and thus weight optimization is considered.

This paper shows the fatigue properties and fracture mechanism of modified 2.25Cr–1Mo steel. In refineries or chemical plants, modified 2.25Cr–1Mo steel is used in hot and high-pressure environments. Recently, a new fatigue problem concerning these facilities has become important, because number of cycles to failure that should be taken into consideration for maintenance has increased to over 107 cycles. For ultra-high-cycle fatigue, interior inclusions in the material are the dominant factor in a fatigue life, but the fracture mechanism for this has not been clearly elucidated. The results of ultra-high-cycle fatigue properties at elevated temperatures are presented. Interior fracture takes place at an ultra-high-cycle region, although many cases show no inclusions in the origins of an interior fracture. Crack growth life is predicted using fracture mechanics, so that life prediction for modified 2.25Cr–1Mo steel is possible.

A multiscale model is developed for fatigue life predictions of elastoplastic solids and structures. The fatigue problem is formulated using a variant of the mathematical homogenization theory developed to account for almost periodic fields. Multiple temporal scales are employed to resolve the solution within a load cycle as well as to predict the useful life span of a structural component. The concept of almost-periodicity is introduced to account for irreversible inelastic deformation, which gives rise to nonperiodic fields in time domain. By this approach the original initial boundary value problem is decomposed into coupled microchronological (fast time-scale) and macro-chronological (slow time-scale) problems. The proposed life prediction methodology was implemented in ABAQUS and verified against the direct cycle-by-cycle simulation.

load. Abstract:The mechanical properties of rubber materials are complex, and the strength problem is getting more and more attention. This paper summarizes the research status of mechanics experiment of rubber materials under dynamic and static load, commented recent years domestic and foreign the progress on the field of rubber uniaxial and multiaxial fatigue. Introduced strength problem research under quasi static load of commonly used constitutive model, selection of constitutive model and determination of parameters status, pointed out the exist problems in experimental study of rubber materials strength.

The fatigue problem in ferroelectric thin films is investigated based on the switched charge per unit area versus switching cycles. The temperature, dielectric permittivity, voltage bias, defect valence and frequency dependent switching polarization properties are calculated quantitatively with an extended Dawber-Scott model. The results are compared with recent experiments. Some features of polarization fatigue and in correlation with parameters of ferroelectric thin films are reported.

In this paper, for the mixed mode fatigue problem, the method of determining testing load was proposed. It is based on the plastic zone size and the limited maximum stress intensity factor by ASTM STANDARD E 647-00. The application method of maximum tangential stress criterion and the stress intensity factor for the finite width specimen was proposed. In the result of applying the method to mixed mode fat gut test for A5052 H34, it obtained the satisfactory experimental results on the stable crack growth.

As a room temperature multi-ferroic with coexisting anti-ferromagnetic, ferroelectric and ferroelastic orders, BiFeO 3 has been extensively studied to realize magnetoelectric devices that enable manipulation of magnetic ordering by an electric field. Moreover, BiFeO 3 is a promising candidate for ferroelectric memory devices because it has the largest remanent polarization ( P r >100 μC cm −2 ) of all ferroelectric materials. For these applications, controlling polarization switching by an electric field plays a crucial role. However, BiFeO 3 has a complex switching behaviour owing to the rhombohedral symmetry: ferroelastic (71 ° , 109 ° ) and ferroelectric (180 ° ) switching. Furthermore, the polarization is switched through a multi-step process: 180 ° switching occurs through three sequential 71 ° switching steps. By using monodomain BiFeO 3 thin-film heterostructures, we correlated such multi-step switching to the macroscopically observed reliability issues of potential devices such as retention and fatigue. We overcame the retention problem (i.e. elastic back-switching of the 71 ° switched area) using monodomain BiFeO 3 islands. Furthermore, we suppressed the fatigue problem of 180 ° switching, i.e. loss of switchable polarization with switching cycles, using a single 71 ° switching path. Our results provide a framework for exploring a route to reliably control multiple-order parameters coupled to ferroelastic order in other rhombohedral and lower-symmetry materials.

The fatigue problem in ferroelectric thin films is investigated based on the switched charge per unit area versus switching cycles. The temperature, dielectric permittivity, voltage bias, frequency and defect valence dependent switching polarization properties are calculated quantitatively with an extended Dawber-Scott model. The results are in agreement with the recent experiments.

This paper shows results of fatigue properties and fracture mechanism of modified Cr-Mo steels. In refinery or chemical plants, Cr-Mo steels are used under hot and high-pressure environments. Recently, a new fatigue problem about these facilities becomes important, because number of cycles to failure that should be taken into consideration for maintenance increases over 107. For the ultra-high-cycle fatigue, interior inclusions in materials are dominant factor in fatigue life, but the fracture mechanism is not made clear completely. Results of the elevated temperature ultra-high-cycle fatigue properties are shown. The interior fracture takes place at ultra-high-cycle region, although many cases show no inclusion in origins of the interior fracture. The crack growth life is predicted using fracture mechanics, so that life prediction for Cr-Mo steels is mode possible.

Effective stress is one of the most important concept in damage mechanics, its application lays a foundation for describing the mechanical behavior of damaged material by the constitutive equation of undamaged material. The present paper discusses the definition of effective stress in fatigue damage process and proposes that the general definition about effective stress in damage mechanics is unsuitable for fatigue damage problem. The authors think that the effective stress should be based on equivalent life in fatigue problem, thereby define a concept of effective stess in fatigue damage according to the concept of residual life and construct a constitutive equation of damaged material. Relationships among fatigue damage evolution law, effective stress variation and the constitutive equation is discussed combining with experiment.

A two-dimensional fretting fatigue problem involving normal and tangential loading of dissimilar elastic bodies in contact is analyzed. The bodies are brought into contact by a monotonic normal load and then a cyclic tangential load is superimposed with the normal load held constant. The Hertz half plane assumption is retained for each body and the region of contact is divided into a central zone of stick and two external regions of micro-slip in each of which the Amontons-Coulomb law of sliding friction is assumed to apply. The effect of the interaction between the normal and shear stresses due to the mismatch in elastic constants is quantified by comparing the present rigid-elastic numerical solution (extreme case) to the Cattaneo-Mindlin closed form solution for elastically identical materials.

The proposed Theory of Metal Fatigue is based on the proposition that the fatigue problem is better understood, if attention is focused on the propagation of a “dominant crack” presumed responsible for the ultimate catastrophic failure of the specimens. The length of the crack at the instant of the catastrophic failure is assumed to be governed by the Griffith condition. The advantage of this formulation appears to be that one is in a position to keep track of the fatigue damage in terms of a growing crack. Consequently, by referring the influence of the different variables on the growth of this dominant crack, it has been found possible to treat the various aspects of fatigue in a fairly systematic manner. The theory distinguishes the order of application of load in two step cumulative damage, and in a fairly simple manner treats the problem of program type loading and random loading and intermixing of stress, temperature and frequency. While analytically the computations for completely random loading became too involved, physically the problem can be fairly well understood in terms of the growth of the dominant crack. One of the fundamental assumptions made is that concerning the mean value of an “internal stress” that is presumed to oppose the motion of dislocations. In the present theory, this stress is formally identified with the “endurance limit” in fatigue. By invoking recovery mechanisms to discuss the decrease of this internal stress as a function of temperature and time, it has been found possible to develop a first order theory of elevated temperature fatigue which gives fair agreement with the test data. The inherent statistical nature of the fatigue problem is attributed in the present theory, to the statistical nature of the internal stresses and the resulting statistical nature of the submicroscopic crack initiation ahead of the dominant crack. Finally an attempt is made to evaluate some of the known shortcomings of the proposed theory.

Cracking of cast iron cylinder liners in some large railway diesel engines is identified as a high strain fatigue problem. A series of low-cycle fatigue tests on three cast irons is reported. An improved material, in which the cooling rate in the critical region of the cylinder liner is slower than normal, has been produced and is shown to be clearly superior to two cast irons used extensively in service. This superiority is due to an improved resistance to both fatigue crack initiation and propagation.

The behaviour of mild steel under conditions of reversed bending in the inelastic range at relatively slow rates of cycling, falls into the category of the low endurance fatigue problem in metals, where failures occur within 105 cycles. This investigation is concerned with an examination of material behaviour in reversed bending (i.e. pure bending) at three frequencies——1, 10 and 100 c/min——and strain ranges in the region from 0.5-12 per cent. Axial extension assumed some significance during the tests at the larger strain ranges, as did cyclic heating at the higher frequency. Some adjustments are made to take account of the effects of axial extension in the tests at the two lower frequencies. A moment-curvature relationship for the material in a cyclic state is established along with a fatigue resistance law for the range of deformations considered; the former being restricted to cyclic operations in the range from 1 to 10 c/min. An indication is given, supported by some experimental evidence, of how the moment-curvature relationship and fatigue resistance law can be used to predict the behaviour of mild steel structural components subjected to the type of loading under consideration.

The effect of the irradiation environment on the microstructure of materials is studied. A major part of the initial activity in this area will be aimed toward evaluating the importance of pulse effects on microstructural development. The development effort that is necessary to cope with the high cycle loading of the first wall structure is studied. The loading pulses are expected to range from 1 to 20 per second (3 x 10/sup 7/ to 6 x 10/sup 8//year), thus creating a high cycle fatigue problem for any long-lived first wall structure. The interrelationship between specimen and component testing is a major issue in this section. Static mechanical property requirements are also considered here. Lithium compatibility is treated. The final section integrates the conclusions reached in the body of the report into a unified strategy that suggests a particular effort level to support major program milestones.

A fatigue test was run on stainless steel pressure release tubing to determine fatigue properties and stress levels caused by mechanical vibration at the resonant frequency in air. It was found that the cyclical stress level was low, on the order of 250 psi, and no fatigue problem was evident.