Influence Of Cyclic Loading Research Articles

Influence of Cyclic Loads on the Fracture Resistance of Pipe Steels and their Welded Joints in Hydrogen-Sulfide Media

It is shown that the high resistance of 20, 30KhMA, and 12Kh21N5T steels to hydrogen-sulfide stress corrosion cracking does not guarantee their high resistance to corrosion fatigue fracture in the NACE solution (wt.%): 5% NaCl + 0.5% CH3COOH + H2S saturated; pH 3–4, 20 ± 3°С. It is shown that the increase in the amplitude of asymmetric cycles causes a more significant decrease in the durability of these steels than the increase in the average value of stresses. We reveal a significant influence not only of hydrogen embrittlement but also of corrosive processes on the fracture of welded joints in the NACE solution. It is shown that this is caused by the growth of their microelectrochemical heterogeneity in the corrosion process, which promotes the localization of corrosive defects.

An Influence of Step Cyclic Loading due to Torsion on Tensile Curve Variation

The paper presents experimental results of tests carried out at room temperature on power engineering steel: 10H2M (11CrMo9-10) using thin-walled tubular specimens under biaxial stress state. The loading programme comprised different types of deformation, i.e. monotonic tension and cyclic torsion in the form of symmetric or asymmetric step-increasing strain amplitude. The main task of the paper was focused on investigation of an influence of the cyclic loading parameters on tensile curve variations. The magnitudes of axial strain and cyclic shear strain amplitude were small and did not exceed 1%. An analysis of the results showed a significant reduction of the axial stress (even equal 90% for the torsional amplitude ±0.8%, in both cases of cyclic loading). An influence of torsion frequency on the tensile stress curve was discovered within the range from 0.005Hz to 0.5Hz.

Influence of Cyclic Load during Curing and Crack Bridging on Repair of Fatigue Crack using CFRP strip

Influence of Cyclic Load during Curing and Crack Bridging on Repair of Fatigue Crack using CFRP strip

Influence of variable operating modes of a steam turbine on the growth of creep cracks in the metal of shell parts made of austenitic steel

Results obtained from assessing the crack resistance of type EI-612 VDP steel by testing notched cylindrical samples under the temperature and stress conditions simulating the loading of metal in shell parts in variable operating modes of a steam turbine are presented. Recommendations for conducting variable operating modes and for the time of carrying out operational checks are given taking into account the influence of cyclic loading on the growth of cracks.

Modification of simple deformation processes of metallic materials by means of cyclic loading

The paper presents experimental results concerning evaluation of an influence of cyclic loading on material behaviour under monotonic deformation. Tests were carried out on pure copper and P91 steel. The experimental programme contained the torsion–reverse–torsion cycles superimposed on the monotonic tension. It is shown that the torsion–reverse–torsion cycles associated with monotonic tension caused essential variations of the tensile characteristic. For both materials, a significant decrease in the tensile stress can be observed. The effects observed during monotonic and cyclic loading combinations were theoretically described for the 2024 aluminium alloy using the Mróz and Maciejewski model.

Kompozyty z wloknami naturalnymi na osnowie recyklatu polipropylenu

The processing by reactive extrusion method of composites based on virgin polypropylene and its recyclates filled with fibers of jute, sisal, hemp or cottonized flax has been presented (Tables 1 and 2). The influence of the addition of three different compatibilizers and fiber alkalization on the properties of the obtained materials was evaluated. The basic mechanical and process properties (Tables 3, 4, Figs. 2-13) as well as water absorption (Fig. 1) were determined and the influence of cyclic loading on them estimated. The potentials and applicability of these composites were also presented.

Evaluation of self‐activating temperature influence on cracks initiation in GRP laminates

AbstractThe paper deals with problems of fatigue processes of GRP laminates under the influence of cyclic loads. An important aspect which takes place in laminate fatigue with polymer matrix is self‐activating temperature generated by friction. As it has been shown in previous authors' research, the phenomenon has significant influence on laminate behavior, also, when self‐activating temperature comes to glass‐transition temperature, which begins transition from elastic to viscoelastic material model. After passing over of this temperature the stiffness decreasing is supervised, that can lead to more quick propagation of faults (especially delaminations) and decreasing of life cycle of composite laminate element. The aim of the presented paper is simulation research of fatigue processes with taking into consideration self‐activating temperature and rheology of material. In the research four cases are analyzed, in which layers rotation, self‐activating temperature increasing and changes of rheological model were taken into consideration. As the research shows, the self‐activating temperature has significant influence on fatigue processes, because it can cause transition of the rheological model of the material. In the future research an experimental verification of the model is planned. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Predicting the influence of overload and loading mode on fatigue crack growth: A numerical approach using irreversible cohesive elements

This paper describes an irreversible cohesive zone model to simulate fatigue crack growth. The model includes a three-dimensional (3-D) cohesive law that follows a distinct loading/unloading path and a damage evolution mechanism that reflects a gradual degradation of cohesive properties of the material under the influence of cyclic loading. To overcome convergence difficulties arising from nonlinearity of the cohesive zone model, the stabilization technique and the viscous regularization of the constitutive law are employed. For high-cycle fatigue applications, a damage extrapolation scheme is adopted to reduce computational cost. The irreversible cohesive zone model is implemented in the finite element software ABAQUS through a user defined subroutine and is used to predict fatigue crack growth in a compact-tension-shear (CTS) specimen with an emphasis on the extrinsic influence of overload for different loading modes. The numerical results show good agreement with experimental records documented in the open literature and capture the essential features of fatigue crack growth for various loading conditions. This indicates that the irreversible cohesive zone model can serve both as an accurate and efficient tool for the prediction of fatigue crack growth.

Fatigue Properties of Steel with Increased Atmospheric Corrosion Resistance

The paper deals with the influence of cyclic loading (tension-compression, bending and torsion) on the course of the fatigue life and the fatigue limit of advanced low-alloyed strip steel with increased atmospheric corrosion resistance. The tested steel shows, besides very good mechanical properties (Re 380 MPa, A5 30%), also very good fatigue resistance and its fatigue limit/ultimate tensile strength ratio is above 0.5. These properties are provided by a favourable fine-grained structure of the tested steel.

About the Calculus of the Materials and Process Equipment Deterioratio

In this second part of the paper, one puts into evidence the factors wich influence the fatigue resistance and the fatigue limit of materials (the frequency of applied load, mean stress, residual stresses, voids or cracks), as well as the influence of cyclic loading onto the monotonic stress � strain curves properties. On the basis of the principle of critical energy one have been established some relations for the influence of mean stress and residual stress about the fatigue strength and fatigue limit. In the same time one puts into evidence the influence of cracks, of the loading direction and of the type of loading one the fatigue limit.

Influence of Cyclic Loading on Fiber Post and Composite Resin Core

From a selection of four kinds of post and core systems, including a fiber post and composite resin core, the purpose of this study was to determine the most effective system for the restoration of endodontically treated teeth with 0 mm of coronal tooth structure. For experimental abutment teeth, typical human maxillary central incisor teeth were modeled using bovine mandibular incisor teeth. By means of a static loading test, the four restoration systems were evaluated and compared in terms of failure load and failure mode. Further, by means of a cyclic loading test, these systems were assessed in terms of durability. For fiber post and composite resin core, it excelled from the standpoints of failure load and failure mode, and fared favorably too in durability after cyclic loading test. For composite resin post-and-core, it also showed excellent results for both failure load and failure mode in static loading test, but durability significantly decreased with cyclic loading. Taken together, the fiber post and composite resin core was found to be most effective from the standpoints of failure load, failure mode, and durability.

Tangent Poisson's ratio of high-strength concrete in triaxial compression

Based on a carefully arranged experimental programme, the paper studies the variation of the tangent Poisson's ratio of high-strength concrete with a uniaxial compressive strength of 67 MPa (100 × 200 mm cylinder) under various confining pressures in triaxial compression. It shows that the high lateral confinement can significantly reduce the initial value of the tangent Poisson's ratio as compared with that of the uniaxial compression, and the tangent Poisson's ratio at failure also decreases notably with the increase of the lateral confining pressure. Therefore the tangent Poisson's ratio of high-strength concrete depends on not only the axial stress but also the lateral confinement. A simplified expression based on the experimental results is then proposed to define this variation. The influence of cyclic loading in triaxial compression is also investigated; this shows that the lateral versus axial strain relation of high-strength concrete during the cyclic loading essentially follows the general trend of the monotonic loading.

Application of magnetic and electromagnetic-acoustic methods for assessing plastic deformations under cyclic loading of annealed intermediate-carbon steel

The influence of cyclic loading of annealed steel 45 during low-cycle fatigue on changes in its magnetic characteristics, in particular, the coercive force and the residual magnetic induction, for the major and minor magnetic-hysteresis loops and on changes in the propagation velocity of a longitudinal acoustic wave is studied. The sensitivity of the considered physical characteristics to the value of plastic deformation stored under cyclic loading in the region of both large and small strains is determined. The residual mechanical properties displayed after cyclic loading are determined, and the steady-state correlations between the coercive force measured on minor hysteresis loops in weak fields (the Rayleigh region) and the remanent clongation are obtained. The possibility of monitoring the stored plastic deformation and assessing the residual life of a material during its cyclic loading from the values of its magnetic parameters is shown.

Lifetime calculation under multiaxial random loading with regard to microcrack growth*

Abstract Generally, most machine parts are loaded with a combination of different variable forces and moments which often causes a state of multiaxial stress in the fatigue-critical areas of the parts. In most cases, a nonproportional cyclic multiaxial state of stress occurs. Compared to in-phase loading, multiaxial loading with a phase shift between the stress components and a load ratio of τa/τa ≈ 0.5 between tension/compression and torsion leads to a significant influence on the fatigue lifetime. The reason is the changing direction and rotation of the principal stresses during one cycle. In this paper, a model is designed to simulate the damage process based on the growth of microcracks under the influence of cyclic loading. Crack growth is initially dominated by shear stresses leading to microstructurally short cracks (stage I) and continues to grow under the influence of normal stresses (physically short cracks). The results of the lifetime estimation generated by means of the new concept based on microcrack growth are compared and verified with those experiences obtained from multiaxial fatigue testing.

Lifetime simulation under multiaxial random loading with regard to the microcrack growth

Generally, most machine parts are loaded with a combination of different variable forces and moments which often causes a state of multiaxial stress in the fatigue critical areas of the parts. In the most cases, a non-proportional cyclic multiaxial state of stress occurs. Compared to the in-phase loading, a multiaxial loading with a phase shift between the stress components and a load ratio of τ a/ σ a≈0.5 between tension/compression and torsion leads to a significant influence on the fatigue lifetime. The reason is the changing direction and rotation of the principal stresses during one cycle. In this paper, a model designed to simulate the damage process based on the growth of microcracks under the influence of cyclic loading is presented. The crack growth is initially dominated by shear stresses leading to microstructurally short cracks (stage I) and continues to grow under the influence of normal stresses (physically short cracks). The results of the lifetime estimation generated by means of the new concept on the basis of microcrack growth are compared and verified with those experiences obtained from multiaxial fatigue testing.

Influence of Cyclic Loading on Inhomogeneous Deformation Behavior Arising in NiTi Shape Memory Alloy Plate

The aim of present paper is the investigation of relationship between inhomogeneous deformation behavior and macroscopic deformation behavior arising in SMA during cyclic loadings. Firstly, a test system was constructed on the basis of Digital Image Correlation in order to measure inhomogeneous deformation behavior. Secondary, measurements of the inhomogeneous deformation behavior (local strain distribution) arising in 50.5Ni49.5Ti plate were tried during cyclic tensile loading–unloading in the region of pseudoelastic temperature. From some results, it is seen that the inhomogeneous deformation behavior sensitively changes according to the state of loadings (i.e., number of cycle, history of loading and so on). Also, the macroscopic deformation behavior for SMAs is strongly affected by the inhomogeneous deformation behavior. It is very important for application of SMA to investigate the relationship between macroscopic deformation behavior and inhomogeneous deformation behavior.

Impact of spatial periodic bending and load cycling on the critical current of aNb3Sn strand

Differences in the thermal contraction of the composite materials in a cable in conduit conductor(CICC) for the International Thermonuclear Experimental Reactor (ITER) in combinationwith electromagnetic charging cause significant axial, transverse and bending strains in theNb3Sn layer. These high strain loads degrade the superconducting properties of a CICC. Here we reporton the influence of periodic bending load, using different bending wavelengths from 5 to 10 mm ona Nb3Sn powder-in-tube processed strand. The strand axial tensile stress–strain curve, the criticalcurrent versus applied axial strain results, the influence of cyclic loading on the RRR andassessment of the current transfer length from AC loss measurements, required for theanalysis, are presented as well.For the strand under investigation, we find an influence of bending strain on theIc that corresponds well to the predictions obtained from the applied classical relations,distinguishing ultimate boundaries of high and low interfilament electrical resistance. Thereduction versus applied bending strain is similar for all wavelengths and equivalentto the low transverse resistance model, which is consistent with the estimatedcurrent transfer length. The cyclic behaviour in terms of critical current andn-value involves a component representing a permanent reduction as well as afactor expressing reversible (elastic) behaviour as a function of the applied load.The results from the set-up enable a discrimination in performance reduction per specificload type and per strand type. In this paper, we discuss the results of the pure bendingtests.

Simulation of microcrack growth for different load sequences and comparison with experimental results

Generally, most machine parts are loaded with a combination of different variable forces and moments which often causes a state of multiaxial stress in the fatigue critical areas of the parts. In this paper, a model designed to simulate the damage process based on the growth of microcracks under the influence of cyclic loading is presented. The crack growth is initially dominated by shear stresses leading to microstructurally short cracks (stage I) and continues to grow under the influence of normal stresses (physically short cracks). The model is applied to tubular specimens of the aluminum alloy AlMgSi1, steel SAE 1015 and notched specimens of 42CrMo4V which are subjected to multiaxial random loading and loading sequences of high–low/low–high stress or a consecutive loading of torsion–tension/compression and tension/compression–torsion for various loading sequences. In terms of the microcrack distribution as a function of their orientation, the simulated crack growth behaviour reveals a close match with the experimental results. The results of the lifetime estimation generated by means of the new concept on the basis of microcrack growth are compared and verified with those experiences obtained from multiaxial fatigue testing.

木造軸組工法耐力壁の静的・動的性状に関する実験的研究

Static and dynamic loading tests were carried out in 8 types of shear walls of wooden post and beam construction. Comparative analyses of the results proved the followings with regard to "static and dynamic properties" and "influence of cyclic loading". In the all types, the dynamic load exceeded 1.1-1.5 times as much as the static load even in small displacement. Regarding the maximum load, the static and dynamic loads were almost the same in wooden elements, and the dynamic load was larger than the static load in inorganic elements. "δu" of the all types and "δy" of the wooden elements were smaller under the dynamic load than under the static load. The failure type of wooden boards changed from "pull-out of nails" to "mixture of punch-outs" under the dynamic load, and the others had no change in the static and dynamic loads. Through the influence of cyclic load, the maximum load of the static loading test of plywood and inorganic boards decreased at 10%-20% range.

Influence of the intensity and duration of cyclic loading on the tribotechnical characteristics of steel

We analyze the results of evaluation of the influence of cyclic loading on the wear rate of 45 steel under conditions of unilateral sliding in contact with the counterbody made of the same steel. It is shown that the presence of both low and high levels of cyclic loads relative to the fatigue limit leads to a decrease in the tribotechnical characteristics of the investigated steel. In author’s opinion, this is explained by the deterioration of the conditions of contact sliding caused by the fatigue damage to the surface layer. The periods of initial hardening, crack initiation, and its growth typical of “pure” fatigue are also present in the dependences of the wear rate on the number of loading cycles in the case of superposition of fatigue and friction.