SN Curves Research Articles

Long term bridge monitoring

Cette etude repose sur la mise au point et l'utilisation du systeme REVE, systeme d'acquisition des effets du trafic routier, sur de longues periodes d'un an a plusieurs annees. Le but est de mesurer globalement de facon experimentale, les effets dynamiques de trafics routiers reels en mesurant des extrema de deformation sur un certain nombre de details a l'aide de reseaux de capteurs intelligents. Il est possible ainsi de disposer d'une information riche, (etablie sur une longue duree), sous forme d'histogrammes de depassement de niveaux et de rainflow. Les amplitudes extremes des effets, en fonction de differentes periodes de retour sont deduites des histogrammes de depassement de niveaux au travers d'ajustements de la formule de Rice, Le calcul du dommage en fatigue issu des histogrammes rain-flow, de la loi de Palmgren―Miner et des courbes S-N est affine par l'utilisation de donnees portant sur de longues periodes de 6 mois et plus au lieu d'une periode habituelle d'une semaine. Les donnees issues de REVE servent egalement au calcul des coefficients de majoration dynamique. Cet article presente une application du systeme REVE et des differents traitements de donnees pour un pont particulier : le pont de Bruneseau.

A critical plane fatigue model applied to out‐of‐phase bending and torsion load conditions

Fatigue & Fracture of Engineering Materials & StructuresVolume 24, Issue 3 p. 153-164 A critical plane fatigue model applied to out-of-phase bending and torsion load conditions F. Morel, F. Morel Laboratoire de Mécanique et de Physique des Matériaux, UMR 6617, ENSMA, Site du Futuroscope, Futuroscope Cedex, FranceSearch for more papers by this author F. Morel, F. Morel Laboratoire de Mécanique et de Physique des Matériaux, UMR 6617, ENSMA, Site du Futuroscope, Futuroscope Cedex, FranceSearch for more papers by this author First published: 07 July 2008 https://doi.org/10.1046/j.1460-2695.2001.00390.xCitations: 12Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume24, Issue3March 2001Pages 153-164 RelatedInformation

Computational Material Testing of Pre-Damaged Steels by the Continuum Damage Mechanics Model.

The constitutive equation based on continuum damage mechanics is applied to the computational material testing of steel specimens. The material constants for the elasto-viscoplastic deformation and the damage evolution are determined by the test results for unaxial stress-strain behaviors and SN curves in fatigue. The identified constitutive equation is used in the computational material testing for the dynamic tensile behavior of pre-fatigued and pre-strained steel specimens. The effects of pre-fatigue and pre-strains on the tensile strength, breaking strains and absorbed energy are quantitatively well evaluated by the computational testing.

A Proposal Of The FM-SN Graphs VisualisationApplied For A Crack Propagation Process

The SN characteristic which is applied in the fatigue investigations Wohler curve determines the number of cycles necessary for the entire destruction of an investigated element as a function of the load amplitude. The estimation of a crack propagation during a fatigue process can be described by the Paris equation and presented in a form of co-ordinates: the crack growth rate as a function of a stress intensity factor range depending on an exterior load and the exterior geometry of the investigated element, as well as on the geometry of a crack* In this paper the transformation method of the Paris curve into the Wohler curve, in the range of line fracture mechanics, FM, is presented. The obtained FM-SN curves make it possible to compare the fatigue crack propagation results with the SN curves. In the given example, concerning the fatigue crack calculations of the container hatch corners, the FM-SN curves were presented in comparison with the SN standard ones.

Fatigue performance of deep water suspended piping systems

Aspects of the inherent statistics related to loads due to lateral moored vessel movement and steel mechanical properties are investigated in order to obtain reliable parameters to evaluate the long-term non-linear dynamics response of deep water piping systems, related to fatigue analysis. The analysis is based on the application of the SN curve associated with the linear cumulative damage rule proposed by Palmgren-Miner. The dynamic stresses acting on the structure are considered wide band, and statistically represented by a generalized gamma distribution.

Fatigue of Ship Critical Structural Details

During the past six years, a joint government-industry-sponsored project titled Ship Structural Maintenance Project (SMP) has been conducted at the University of California at Berkeley. As part of the SMP, fatigue of ship critical structural details (CSD) has been studied. This paper summarizes developments in the stress range—number of cycles to failure (SN) analysis developed during the SMP. Nominal stress and hot spot stress procedures were employed to evaluate fatigue damage to ship CSD. A “cracked SN curve” approach was developed based on a hybrid SN-FM (fracture mechanics) methodology to evaluate the residual life of cracked ship CSD. The fatigue durability characteristics of repaired CSD was studied. Numerical examples are presented to illustrate these developments.

Intrinsic fatigue curves applied to damage evaluation and life prediction of laminate and fabric material

Modeling of the stochastic fatigue behavior of specimens is made from a knowledge of the intrinsic character of fatigue referred as the intrinsic fatigue curve (IFC). The idea is to predetermine the fatigue behavior of specimens' population such that each sample functions of IFC would correspond to the intrinsic fatigue character of a specimen. The existence proof of IFC is derived from Kolmogorov's theorem for a random function. The form of IFC is obtained for log-normal life distribution functions of specimens subjected to constant-amplitude load histories. Proposed is a linear damage accumulation rule for estimating the life distribution function of a specimen subjected to irregular load histories. For a stationary loading process, the life distribution function is also shown to be log-normal. The relations between the quantile SN curves and IFC are established. The ways of creating IFC from test data and quantile SN curves are illustrated by numerical examples for laminate and fabric material.

Effects of Surface Treatment on the Bending Fatigue Strength of Carburized Spur Gears

This paper deals with the effects of surface treatment on the bending fatigue strength of SCM 415 carburized spur gears. The test gears are hobbed and carburized, then the tooth surfaces are treated by a combination of shot peening, chemical polishing and electropolishing. The residual stress is increased by the surface treatment. The SN curves are obtained from the results of a constant stress amplitude fatigue test, and the enhancement of fatigue strength due to the surface treatment is clarified quantitatively. The fatigue strength is well approximated by an experimental formula which has been proposed to evaluate the strength from the hardness and residual stress. The effect of variations in hardness and residual stress of test gears is eliminated using the formula, and the influence of surface roughness on fatigue strength is evaluated. It is approximately equal to the relative surface condition factor specified in the ISO strength rating formula.

Effects of Surface Treatment on the Bending Fatigue Strength of Carburized Spur Gear.

This paper deals with effects of surface treatment on the bending fatigue strength of SCM 415 carburized spur gears. The test gears are shot peened, chemical polished and electropolished after carburization. The constant stress amplitude fatigue test is performed by using an electrohydraulic servo-controlled pulsating tester. The SN curves are obtained and the enhancement of fatigue strength due to surface treatment is clarified. The effect of surface conditions on the fatigue strength is evaluated quantitatively, and it is close to the relative surface condition factor used in the ISO strength rating formula.

Fatigue Strength of As Welded and Improved Joints of 6N01 Aluminium Alloy Extrusions

In this paper, the fatigue strength of welded joints of 6N01 aluminium alloy extrusions is studied. Less copper content (Cu_??_0.02%) alloys were chosen, taking corrosion resistance to sea water into consideration. Two series of specimens were prepared. One is non-load carrying transverse fillet welded cruciform joint (T-TYPE), and the other has two longitudinal stiffeners welded on both sides of the main plate (L-TYPE). For L-TYPE, three types of specimens, changed in details of end of longitudinal stiffeners from the conventional corner boxing, were arranged. For some specimens, weld toes were ground with a pencil grinder. Using the specimens, fatigue tests under axial tensile loading (R=0) were carried out.In the fatigue test results, evident differences existed. The fatigue strength of ground T-TYPE specimen was highest, and that of as welded L-TYPE ones was lowest. The fatigue strength of as welded T-TYPE specimens was higher than that of ground L-TYPE ones. These SN data were consolidated and yielded to one SN curve, using the equivalent stress, taking the maximum stress into account. The equivalent stress S_??_ was expressed as follows; where Smax=maximum stress, R=stress ratio, m=constant, S=stress range, K=stress concentration factor, Sn=nominal stress range, and SR=residual stress.In the last part of the paper, some techniques for improving the fatigue strength of corner boxing welds are illustrated.

Size Effect in Bending Strength of Carburized Gear Teeth

This paper deals with the bending strength and the size effect of carburized fine module gears. The fine module test gears (m = 1–1.5) are made of a low-carbon alloy steel, and they are carburized to have various effective case depths. The bending fatigue tests are performed using these gears. From the test results, the AGMA recommendation of the effective case depth is confirmed to be valid in view of the bending strength. The SN curves are obtained and they are expressed by the experimental formulas. The fatigue strength of fine module gears are compared with the strength of gear of m = 5, and the size factor is evaluated. In order to make clear the size effect, the fracture mechanics is applied to the fatigue test results. The fatigue life is assumed to be the crack propagation process, and the maximum initial length of crack is evaluated. This crack length is proportional to the thickness of nonmartensitic layer at the fillet. The size effect is discussed on the basis of stress intensity factor and the thickness of nonmartensitic layer.

Fatigue crack growth through partially stabilized zirconia at ambient and elevated temperatures

Fatigue crack growth through magnesia stabilized zirconia at 20, 450 and 650°C has been observed dynamically in a high temperature loading stage for the scanning electron microscope. Crack tip micromechanics parameters were measured using the stereoimaging technique. Fatigue crack growth at ambient temperature was found to be very similar to crack growth through metallic alloys. With increasing temperature, the stress intensity levels in which stable fatigue crack growth could be sustained were found to narrow significantly, until fatigue is expected to not be a valid mechanism of crack growth above about 750°C. Measured crack tip parameters were used to derive the low-cycle fatigue and the stress-cycles to failure characteristics. The latter agreed with measured SN curves. Deformation within the plastic zone was shown to account for the measured value of fracture toughness. The mechanisms of crack growth are discussed.

Environmental effects in fatigue crack initiation and propagation: Comm. Eur. Communities Rep. No 12205 1990, 65 pp

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.

The Fatigue Behaviour of HSLA Non-Load Carrying Spot Welded Joints

AbstractThe results presented in this paper are of practical engineering significance for the design of structures with low load carrying spot welded joints. They indicate that contrary to previously published data, non-load carrying spot welded attachments should be used with caution in some circumstances. Nonload carrying spot welded joints of 2-mm thick HSLA sheets were tested in fatigue. The obtained SN curve was compared to curves for plain specimens and specimens with a hole. The non-load carrying spot welded joints have a significantly lower fatigue limit as compared to plain specimens and even specimens with a drilled hole. The presence of welding defects (pores or deep indentation) seems to increase the fatigue endurance. The data also suggest that the fatigue limit decreases when the sheet thickness or the nugget diameter are increased. Resume Les resultats presentes ont un interet pratique pour la conception de structures comportant des joints soudes par resistance transmettant de faibles charg...

SN curve estimation of fatigue test using experimental regression analysis: Shin, S. and Yano, H. Bull. Natl. Res. Lab. Metrology 1989 38, (1), 7–18

Injection moulded short fibre reinforced composites (SFRC) have variable fibre orientation distribution at every point and are often subjected to multi-axial fatigue loading due to their inherent anisotropic nature. The fatigue properties are known to be significantly dependant on the fibre orientation distribution. Thus, the fatigue simulation of SFRC components poses dual challenges of predicting the local SN curves and also accounting for the multi-axial loading. This paper describes two models extending the Master SN curve approach (doi:https://doi.org//10.1016/j.compositesa.2015.11.038) for multi-axial fatigue modelling of SRFC. The models proposed are adaptations of two existing well-known formulations; namely the characteristic plane approach and the critical plane approach. The proposed models are validated using published experimental data confirming a match with an error less than about 15%. Both the models are compatible with the through process modelling framework of injection moulded SFRCs and thus have significant potential for use during fatigue simulation of SFRC components.

Bending strength of spur gear teeth made of austempered ductile iron.

The use of gears for power transmission is conditioned by the strength as well as the accuracy. The employment of austempered ductile iron is examined from this view point. The test gears are made of ductile irons FCD45 and FCD60. They are austenized at 900°C then austempered at 300 to 400°C. In the austempering process, the bainitic transformation causes size expansion and a considerable tooth profile error of the gears. The profile error can be reduced by austempering at 400°C or employing the ferrite-bainite dual phase ductile iron. The bending fatigue tests are performed by using electro hydraulic servo controlled pulsators, and SN curves are obtained. The higher the austempering temperature, the higher the fatigue strength. The fatigue strength of gears austempered at 400°C is about 520MPa and it is higher than the strength of normalized S45C gears.

Time-dependent nonlinear fatigue analyses of the TLP in the arabian sea environment

The tension leg platform (TLP) is a new concept in the design of platforms. It combines the facilities of both floating, drilling, and production platforms. The deck is secured by vertical tension legs attached to pile foundation templates on the sea bed. An attempt has been made in this paper to calculate the short and long term statistics of the stress response to the natural short and long crested sea and the resulting fatigue damage for certain critical members of a proposed TLP. A probabilistic approach is adopted utilising a spectral method for calculating the number of wave induced cycles at different stress levels. The nonlinear finite square stress element method is used to determine root mean square deflections and root mean fracture in randomly excited TLPs. Program RANDOM is developed to solve various theoretical equations and to evaluate the fatigue life. The basic input to the program consists of material properties, SN—curve and environmental data.

The Effect of Molecular Structure on the Formation of Induced Nematic Phases in Binary Mixtures

Abstract A variety of 4-halophenyl-4′-alkoxybenzoates and 4-alkoxyphenyl-4′-halobenzoates were synthesized, their mesomorphic properties determined and compared with those of the analogous halo anils. The ability of these esters to form induced nematic phases (INPs) in binary mixtures was studied along with a variety of other mesogenic type compounds not having a nematic phase. The contact method was used to screen 258 mixtures for INPs in an attempt to determine which molecular structural features favored formation of this phase in binary mixtures. INPs were observed in many of these mixtures and with a wide variety of structures. Phase diagrams of some of these mixtures were obtained in order to compare the abilities of certain structural features to form INPs. Two types of diagrams were observed. Type I showed a narrow INP range ocurring over most of the composition range between two nearly linear SN and MI curves and was observed only when the two components had similar molecular lengths either short ...

Comparison of SN and HI antibody dose response curves in chickens, rabbits, foals and horses following vaccination with equine influenza vaccine

After vaccination of chickens, rabbits, foals and horses, HI and SN antibody dose response curves were compared for A/Equi 1/Prague and A/Equi 2/Paris strains. The two curves are parallel for a given strain and the relationship of HI and SN titres is constant, whatever the animal species. The distribution of HI and SN titres varies for the two strains. This variation, which is independent of animal species, may be related to the number of sites necessary for the antigenic-antibody response in vitro. It is suggested that the testing of equine influenza vaccine be carried out in the chicken in the light of these results.

Environmental effects on fracture resistant and biaxial fatigue design of aircraft structures

This paper discusses the two interrelated fields of crack initiation and crack propagation by presenting analytical techniques for calculating fatigue damage in biaxially stressed structures along with determining safe inspection intervals for contained crack growth. The equivalent stress concept is used to derive a set of uniaxial stresses that produce the same amount of fatigue damage as the biaxial stress exposure. The distortion energy concept serves as the basis for combining alternating principal stresses by translating the uniaxial SN curves for zero mean stress into a family of concentric ellipses. The major axis bisects the principal stress axes for isotropic materials with invariant directional fatigue performance. The intercept of these ellipses with the maximum alternating principal stress axis defines the equivalent alternating stress at various cyclic lives. Empirical procedures are given for treating problems with varying principal stress directions and areas with directional dependent fatigue performance. The Goodman diagram relates alternating stresses and mean stresses at any constant cyclic life. If two uniaxial Goodman diagrams are constructed on each reference axis, a three-dimensional body can be visualized which intercepts the zero alternating stress plane in a shape identical to that described by the applicable static load criterion. The equivalent mean stress concept is based on the existence of a similarly shaped closed surface at any value of alternating stress. The intercept of this surface boundary with the maximum mean stress axis is the equivalent mean stress. Crack growth rates and residual strength of structure are important items since it is necessary to consider the possible existence of cracks. Static failsafety consists of contained crack growth for reasonable lengths of time and back-up structure providing alternate load paths. The stress intensity factor K, reflecting the distribution of stress in cracked structure, is the basis for computing crack growth. Baseline crack growth data for several material toughnesses and environmental exposures is required for fracture analysis. The method employed consists of calculating stress intensities for various crack lengths in the structure, these primarily being a function of geometry and applied stress distribution. The crack growth curves are constructed by integrating the baseline data for the appropriate corrosive exposure with additional factors applied to allow for scatter in growth rates and load magnitudes.