The proposed methodology was applied to a simplified case of a stamp. The contact pressure sheet/tool calculated at the end of strike allowed the evaluation of the stress state in the tool. This was mainly uniaxial compression with a value of −220 MPa. In order to include fatigueanalysis in the design procedure, the fatigue of cast iron EN-GJS-600-3 was studied at room temperature. The SN curves of this material were established with load ratios R0−2, −1, and 0.1. The SEM micrograph allowed to study the crack initiation and to identify two groups of fracture origins. In the case of material without defects, a debonding of nodular graphite in surface causes crack initiation. However, some micro-shrinkages and big grains of graphite near the outer surface are the main cause of crack initiation in the material with defects. Presence of foundry defects with a size between 100 μm and 1 mm in the 9 mm diameter of specimen is associated with a reduction of fatigue lifetime by a factor of 2. However, this factor is more accentu- ated by the load ratio effect that can reach a factor of 40.
This paper presents the results of a fatigueanalysis of a CF-18 aft wing fold shear-tie lug, which involved multiple crack nucleation sites and short crack growth under complex geometry and loading conditions. A three-dimensional (3D) finite element model was developed to simulate the loading applied in the shear-tie lug test and determine the local stress/strain distribution. Short crack data and the subsequent material model, were specifically developed for the lug material (7050-T7452 forging), in which work the Holistic Structural Integrity Process (HOLSIP) approach was used to correlate the short crack model with material microstructural features, such as constituent particles and porosities. After the shear-tie lug fatigue test, quantitative fractography (QF) was carried out to measure the crack growth size. Based on the failure mechanisms, a simplified single crack model was proposed to analyze this multiple crack growth problem, and the life estimation compared well with the test results.
Abstract. In this research, attempts are made to conduct concrete mus- cle fatigueanalysis of arbitrary motions on OpenSim, a digital human modeling platform. A plug-in is written on the base of a muscle fa- tigue model, which makes it possible to calculate the decline of force- output capability of each muscle along time. The plug-in is tested on a three-dimensional, 29 degree-of-freedom human model. Motion data is obtained by motion capturing during an arbitrary running at a speed of 3.96 m/s. Ten muscles are selected for concrete analysis. As a result, the force-output capability of these muscles reduced to 60% - 70% after 10 minutes’ running, on a general basis. Erector spinae, which loses 39.2% of its maximal capability, is found to be more fatigue-exposed than the others. The influence of subject attributes (fatigability) is evaluated and discussed.
Fatigueanalysis-based numerical design of stamping tools made of cast iron
K. Ben Slima & L. Penazzi & C. Mabru & F. Ronde-Oustau
Abstract This work concerns stress and fatigueanalysis of stamping tools made of cast iron with an essentially pearlitic matrix and containing foundry defects. Our approach con- sists at first, in coupling the stamping numerical processing simulations and structure analysis in order to improve the tool stiffness geometry for minimizing the stress state and optimizing their fatigue lifetime. The method consists in simulating the stamping process by considering the tool as a perfect rigid body. The estimated contact pressure is then used as boundary condition for FEM structure loading anal- ysis of the tool. The result of this analysis is compared with the critical stress limit depending on the automotive model. The acceptance of this test allows calculating the fatigue lifetime of the critical zone by using the S–N curve of corresponding load ratio. If the prescribed tool life require- ments are not satisfied, then the critical region of the tool is redesigned and the whole simulation procedures are reacti- vated. This method is applied for a cast iron EN-GJS-600-3. The stress-failure (S–N) curves for this material is deter- mined at room temperature under push pull loading with different load ratios R0σ min /σ max 0 −2, R 0 −1 and R 0 0.1. The effects of the foundry defects are determined by SEM observations of crack initiation sites. Their presence in tested specimens is associated with a reduction of fatigue lifetime by a factor of 2. However, the effect of the load ratio is more important.
 V. Zerrouki, “Inconel 718 et tenue en fatigue oligocyclique. Influence de
la microstructure et prédiction de la durée de vie”, Mémoire de DRT
Génie des Matériaux, Université EVE, 2000.
 Y. Ohtake, S. Rokugawa, H. Masumoto, “Geometry determination of cruciform type specimen and biaxial tensile test of C/C composites”, Key Eng. Mater., vol. 3, pp. 151-154, 1999.
4.3. Thermal fatigue damage
Cracks initiation localisations are listed in Fig. 11 . The ﬁrst cracks start at areas the thermocouples are placed especially in the zone where 3 thermocouples (including the reference thermo- couple) are positioned (for gradient measurement purpose). The reference sensor is indeed positioned 2 mm inward the edge of the bowl in an area where the thermal gradient is most drastic. After only 250 loading cycles, a crack appears and propagates rap- idly in-depth to reach 9 mm where the crack propagation rate is very much reduced leading to the stabilisation of the crack pro- gress. Four TF cracks appear in the valve recesses zones after 3520 TF cycles. Other cracks appear later at 3550 cycles in another thermocouple localisation and subsequently at 4500 TF cycles in a slightly less stressed zone. It must be emphasised that the cracks initiation and propagation in particular when the cracks are long tend to produce heterogeneous induction heating by altering the electromagnetic ﬁelds. Heating is therefore concentrated around the crack lips (long crack > 7 mm) which may compromise the use of induction in TF testing. Nevertheless, the main objectives of the TF testing rig developed here are validated. The experimen- tal set-up indeed enables to generate a local damage in areas with
3.1 Principle of crack prediction
The computation of the transient stress field is meant as input to a fatigue prediction model, based on the Dang-Van theory, with enrichment and extensions. The fatigue limit domain of the common copper alloy is modeled with a multi-slope Dang Van criterion, as shown in Figure 4. The material characteristics were identified thanks to fatigue tests performed by SNCF on small specimen subjected to cyclic bending loads. In the Dang Van histogram (mesoscopic shear stresses according to hydrostatic pressure), the cyclic stresses path of any point of the CW can be plotted. The criticality of a given cycle due to a train passage is quantified by a scalar called criticality (“Cd” in the figures). This criticality Cd has been directly linked to an expected lifespan before crack initiation via an innovative method detailed in a later publication.
The monocycle ZM model for SMA is extended to account for thermomechanical coupling. It is implemented into the finite element code Cast3m, considering strong coupling between me- chanical and thermal equations. Quantitative and qualitative comparisons between experiments and simulations at low strain rates show good agreement for both thermal and mechanical responses. However, for high strain rates the agreement is achieved only qualitatively. This discrepancy may be explained by the occurrence of the localization of the martensitic transfor- mation which is not considered in our model. The model accounts for intrinsic dissipation, which explains the formation of the hysteresis loop even for quasistic loading conditions, and latent heat, which was found to be predominant when solving the heat equation. The lim- ited influence of dissipation on the temperature of the material should not be interpreted as a complete absence of intrinsic dissipation. Then, an experimental and theoretical study of the thermomechanical coupling in SMAs in the cyclic pseudoelastic regime has been provided. First, an experimental analysis has been performed using superelastic NiTi wires subjected to cyclic loadings. The obtained results give an explanation of the evolution of the mechanical response with the strain rate. Namely, the analysis of the thermal results allow to associate this depen- dence to the thermomechanical coupling. For example, the stabilized cycle is greatly influenced by the thermomechanical coupling, because phase transformation yield stresses and slopes as well as hysteresis area change with strain rate. In addition, it is shown that the hysteresis area follows a non-monotonic evolution with the strain rate for both the transient and the stabilized responses and that the maximum is reached for a strain rate of 1.10 −3 s −1 . Second, in order to account for the cyclic thermomechanical coupling, a model was developed and validated against experimental data. A good correlation is achieved for both the transient and the stabilized me- chanical responses for all strain rates. The thermal response is also reproduced, but with lower accuracy especially at high strain rates. The simulation reproduces the non monotonic evolution of the hysteresis area at the stabilized cycle, with a maximum error of 8 %.
tered with a pass band filter. The software is devel- oped with Labview. It allows to choose many stim- ulation parameters in order to have different stimu- lation pulse shapes and sequences. The current am- plitude can vary from 0 mA to 100 mA, the duration of pulses can be set from 500 µs to 2000 µs, the fre- quency of pulse train from 10 Hz to 100 Hz. The shape of pulses have been chosen among the most common ones in the literature (Watanabe et al., 2000; Karu et al., 2002) such as Monophasic ones, Bipha- sic ones, Dual Biphasic ones, Asymetric Biphasique ones and Doublet Nlet ones. The stimulation and rest duration and the kind of fatigue treatment are also ad- justable. Many graphics have been added in order to visualize the electrical activity such as the representa- tion of one period of stimulation pulses, the ongoing EMG signal in real time, the M wave reference and fatigueanalysis results.
This paper describes a microstructural-based high cycle fatigue behaviour model applied to cast Al-Si alloys used in an automobile context. These materials are characterized by the presence of di fferent microstructural heterogeneities at different scales: the aluminium matrix (DAS/SDAS and the precipitation hardening level), inclusions (Si particles and intermetallic) and casting defects (porosity). It is shown that the effects of these factors on the HCF damage mechanisms are important and can depend on the loading mode. A multiaxial fatigue test campaign has been carried out using three cast aluminium alloys, fabricated by different casting processes (gravity die casting and lost foam casting), associated with several heat treatment(T7 and Hot Isostatic Pressing-HIP). The HIP treatment is used to eliminate or minimise the porosity. The first part of the article is dedicated to the experimental characterization of the HCF damage mechanisms. With regard to the e ffect of the casting defects, a study of natural fatigue crack growth and artificial long crack growth is presented and subsequently used to choose an appropriate fatigue strength criterion to take into account the effect of defects, for different loading modes (tension, torsion and combined tension-torsion). Finally, a flexible modelling framework, providing the possibility of combining any two suitable criteria, which leads to the construction of a multiaxial Kitagawa-Takahashi diagram, is used.
Complex activities require a sustained mental effort that causes cognitive fatigue. This fatigue may be the source of errors by disrupting action control. In this study, we examined its effects on reactive and proactive action control. Two groups performed a Simon task (a conflict task) after completing a fatigue-inducing task (a dual task combining a 2-back task and a parity judgment task, Borragàn et al., 2017) in which the cognitive load was high or low. In order to measure reactive and proactive control, we evaluated the correction rate, distributional analyses and the Gratton effect based on electromyographic analyses. We observed that fatigue have only impaired proactive control. Participants in the high load condition were less able to adjust their behavior after observing a conflict. These results are in line with previous studies which posit a change to less demanding strategies when participants became mentally
1. Il s'agit d'une rupture par fatigue du reste prévisible.
2. Vu que pour les raisons fonctionnelles, il ne semble pas possible de ménager un congé susant entre les deux portées, un remède serait d'utiliser un acier plus dur, par exemple 42CrMo4 trempé et revenu.
As a conclusion, only a few studies investigated fatigue striations while they could bring new information on the role of SIC on the lifetime reinforcement under non-relaxing loadings. Furthermore, the studies differed in terms of material, loading condition and sample geometry, which makes difficult any generalization to NR. Additional fatigue tests have therefore to be carried out at different loading ratios and temperatures. The next section presents these new fatigue tests. The experimental setup is first provided. Then, results are given and discussed. Concluding remarks close the paper.
4. Band-Pattern Evolutions and Material Fatigue Criterion
It is seen in Chapters 2 and 3 that the Lüders-like band formation and evolution (band-front motion) have significant effects on the fatigue behaviors of pseudoelastic NiTi polycrystalline strips under uniaxial tension –– the cyclic band nucleation/annihilation triggering the localized martensitic phase transformation leads to more microstructure degradation and shorter fatigue lives than the cyclic homogeneous deformation. Moreover, a fatigue criterion should adopt the local material responses rather than the structural global/nominal responses in order to accurately predict the fatigue life; in particular, it is found that the local strain amplitude is a good indicator on the fatigue life (see Fig. 3.4(b)) when the specimens are loaded with a similar maximum stress level and without large temperature variations. However, in the real applications of SMAs, there are a number of factors that need to be considered, such as the material’s microstructure effects [4, 42, 46, 49, 93, 94], experiment temperatures [4, 5, 95, 96], levels/amplitude of the applied stress/strain [4, 8, 12, 37, 42, 46, 50, 57, 81, 95, 96], and loading rate (frequency) [4, 9, 22, 51, 89, 96, 97], etc..
Considering several samples, we observe that the nuclea- tion defect is located between sample surface and 6 mm far from the surface and its maximum size is 300 mm in diameter. As shown in Fig. 3, the EDSX analysis demonstrates that these defects contain more sulphur than the rest of the material. Therefore, they correspond to overvulcanised zones in the section. Surface of Zone 1 is rough; it corresponds to a stable propagation of the crack and surrounds the defect. Its size can reach 6 mm in diameter. Zone 2, which surrounds Zone 1, represents the rest of the fracture surface. It corresponds to an unstable propagation of the crack. The surface is relatively smooth and slight bifurcations of the crack can be observed. No fatigue striations are observed for every loading condi- tions considered in this study.
MVM), centré sur le sentiment du travail et de la fatigue comme devoir moral.
Ce premier modèle peut rappeler certains aspects du modèle de la « dilapidation » évoqué par Olivier Schwartz. Il est particulièrement net dans trois entretiens, réalisés à MVM auprès d’hommes respectivement âgés de 25 ans, de 34 ans et de 51 ans. Dans les trois cas, la nécessité pour le travail effectué de la force musculaire et la forme physique sont mis en avant. « Q : Est-ce qu'un débutant pourrait faire votre travail? R : Oui, s'il est assez costaud, il peut le faire. Je dis pas qu'il faut être superman, mais il faut quand même tenir huit heures.... Quand on passe des pièces comme on est en train de passer là, à cette heure-ci, elles font deux mètres de long sur cinquante centimètres de large, pour passer ça dans la journée, il faut quand même tenir » (34 ans) ; « Q : est-ce que vous trouvez que votre travail est fatigant ? R : Pour l'instant, non... je suis assez sportif, tout ça... donc ça va » (25 ans) ; « C'est sportif, voilà... j'aime bien [...]. Le jeune, il fatigue plus vite, parce qu'il n'a pas l'habitude » (51 ans). Une certaine fierté de la production réalisée est également exprimée dans les entretiens : « En une journée de huit heures on arrive à faire dix mille portes » (25 ans). Pour ces trois personnes, la plainte de fatigue est très faible et aucun problème de santé n'est signalé à l'enquêteur. Cette négation de la fatigue et de l'usure est liée à la fois au refus de reconnaître sa faiblesse et à la nécessité de tenir pour garder sa place : « Vous n'êtes plus bon, on vous balance » (51 ans). La direction semble d'ailleurs utiliser cette idéologie à son profit en stigmatisant ceux qui ne peuvent plus tenir le rythme : « Ici, les gens qui ne peuvent pas faire grand chose, ils les appellent des handicapés, là s'ils peuvent leur trouver une place plus cool, ils leur trouvent. Il y a le gardiennage, il y a... » Le recours médical pour fatigue est donc plutôt faible et la représentation dominante est qu'il faut tenir jusqu'à la retraite. Si un âge plus précoce pour le départ en retraite (55 ans) est souhaité, c'est alors non pas parce que l'on en peut plus, mais plutôt pour pouvoir en profiter en bonne santé, avant une usure totale, et pour laisser la place aux jeunes. La retraite n'est pas la paresse mais au contraire le repos et surtout la liberté bien mérités.