Ein Modell für verantwortungsvolles Handeln in der IT-Organisation

In der Betriebswirtschaft ist verantwortungsvolles Handeln, repräsentiert durch Konzepte wie Corporate Social Responsibility (CSR), Corporate Citizenship (CC) oder Nachhaltigkeit/Sustainability, eine in Forschung und Praxis breit diskutierte Thematik. Eine umfassende Übertragung der Problematik auf das IT-Management hat jenseits von isolierten Einzelthemen wie „Green IT“ etc. jedoch noch nicht stattgefunden. In diesem Beitrag wird deshalb ein Modell vorgestellt, welches auf der einen Seite einen ganzheitlichen Rahmen für verantwortungsvolles Handeln in der IT-Organisation eröffnet, und auf der anderen Seite Stellschrauben für die aktive, verantwortungsvolle Beeinflussung des Wettbewerbsumfelds aufzeigt. Konkretisiert wird das aufgezeigte Modell anhand verschiedener Maßnahmenfelder zur Umsetzung verantwortungsvollen Handelns

Disturbance induced by surface preparation on instrumented indentation test

International audienceSurface preparation, which may induce considerable sample disturbance, plays an important role in instrumented indentation test (IIT). In this study, the sample disturbance (mainly divided into residual stresses and plastic strain) induced by the surface preparation process of instrumented indentation test specimens were investigated with both experimental tests and numerical simulations. Grazing incidence X-ray diffractions (GIXRD) and uniaxial tensile tests were conducted for characterizing the residual stresses and high plastic strain in the top surface layers of a carefully mechanically polished indentation sample, which, in the present work, is made of commercially pure titanium. Instrumented indentation tests and the corresponding finite element simulations were performed as well. For comparison, a reference sample (carefully mechanically polished & electrolytically polished) which represents the raw material was prepared and tested. Results showed that a careful mechanical polishing procedure can effectively reduce the level of residual stresses induced by this process. However, the high plastic strain in the surface region imposed by the polishing process is significant. The induced plastic strain can affect a depth up to 5 µm, which is deeper than the maximum penetration depth hmax (3 µm) used for the instrumented indentation tests. In the near surface layer (in the range of depth about 350 nm), the plastic strain levels are fairly high. In the very top layer, the plastic strain was even estimated to reach more than 60%. The simultaneous use of indentation tests and numerical simulations showed that the existence of high plastic strain in the surface region will make the load vs depth (P–h) curve shift upwards, the contact hardness (H) increase and the contact stiffness (S) decrease

Mechanical characterization of a SMATed 316L stainless steel: use of cyclic nanoindentation

The study of nanomaterials, which are characterized by a typical grain size below 100 nm, is nowadays a very active and dynamic branch of materials science research. The starting point of this great interest, which led to numerous studies and the development of new technologies, is the famous publication of H. Gleiter in 1989. It has been established that metallic materials with a grain size in the ultrafine (<500 nm) or in the nanocrystalline (<100 nm) regimes, exhibit remarkable mechanical and physical properties. This is due of the small grain size of these materials, or more precisely to the very large volume fraction of grain boundaries induced by these narrow grains. From a mechanical point of view, these materials present higher yield strength and hardness, as well as greater wear resistance. A major challenge today is to quantify the real mechanical response of nanomaterials. Actually, most of the elaboration processes of nanomaterials have none negligible effect on their mechanical response, and appropriate tests have to be developed to characterize the mechanical properties of these materials. The aim of this paper is to characterize the mechanical response of 316L stainless steel treated by SMAT (Surface Mechanical Attrition Treatment) using nanoindentation. After SMAT, this stainless steel looks like a multilayer structure characterized by a grain size gradient from the top treated surface to the bulk of the materials. Whereas the global mechanical response of the SMATed material can be analysed by classical tensile tests, precise nanoindentation tests have to be performed in order to reach local information on the nanocrystalline layer formed at the top surface of the material during the treatment. To this end, cyclic nanoindentation experiences have been performed over the cross section of a SMATed sample. A finite element model was then developed to simulate indentation tests, and to determine afterwards the constitutive law for each sublayer. It is thus possible to find a correlation between the microstructure evolution and the mechanical response of the material

Characterization of Residual Stresses and Accumulated Plastic Strain Induced by Shot Peening through Simulation of Instrumented Indentation

International audienceIn this study, a method based on finite element (FE) simulation was proposed for characterizing simultaneously residual stresses (RS) and accumulated plastic strain (PP) induced by shot peening process. Through a series of simulations of instrumented indentation, contour plots of several parameters, as maximum load, contact hardness and contact stiffness, were computed. By superposing them pair-wisely, RS and PP mixed together could be characterized simultaneously. In order to verify the method, several simulations with different combinations of RS and PP were performed. Results showed that the method is promising but remains to be tested on experimental acquisitions

A robust cyclic elastoplastic constitutive framework for fatigue life analysis

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Cyclic inelastic constitutive equations and their impact on the fatigue life predictions

International audienceCyclic plasticity and viscoplasticity constitutive equations are revisited in the context of fatigue life analysis of components submitted to small strain amplitudes but high strain ratio. The model used is based on a series of back stresses, each of them containing a threshold in the dynamic recovery term. Capability to correctly reproduce the cyclic softening and the limited mean stress relaxation is particularly examined, with the help of analytical solutions for uniaxial conditions. Comparisons are made with available experimental data on a Titanium alloy and a Nickel base superalloy, both in terms of the stabilized mean stresses and for the corresponding fatigue life prediction

Self-consistent modeling of the mechanical behavior of an austenitic stainless steel under low cycle fatigue loading

International audienceExperimental results of low cycle fatigue (LCF) tests, with different total strain amplitudes from ±0.5% to ±1.25%, show that the studied austenitic stainless steel 316L undergoes an initial hardening followed by a large softening range, and then reaches stress stabilization until fracture. Furthermore, stress analysis highlights obvious strain range effect for this material during cyclic loading. In this work, an elastic-inelastic self-consistent model for polycrystals is used to simulate the mechanical behavior of the material under uniaxial low cycle fatigue loadings. A modified kinematic hardening variable χ^s and a set of isotropic hardening variables k^s, associated with state variables of crystal slip systems, are proposed to describe the hardening/softening behavior of the material. Along with the parameters concerning grain/matrix interaction law and homogenization method, material parameters of kinematic and isotropic hardenings are identified using optimization methods. With the identified parameters, it is shown that the modified model is able to well describe the cyclic hardening/softening behavior as well as the strain range effect under uniaxial loading

Cyclic behavior of gradient microstructure generated by Surface Mechanical Attrition Treatment for an austenitic stainless steel

International audienceLow cycle fatigue (LCF) behavior of materials processed by SMAT (Surface Mechanical Attrition Treatment) was studied for a stainless steel 316L. SMAT was used to generate gradient microstructure in cylindrical fatigue specimens. Fully reversed strain controlled LCF tests were performed with different strain amplitudes. Hysteresis loops corresponding to different depths from the treated surface were indirectly obtained from the loops obtained by the fatigue tests for SMAT treated and untreated specimens. The results show that the influence of SMAT on cyclic behavior of material is effective mainly during the first several cycles, and it is gradually reduced with the increase of number of cycles. The results also show that SMAT causes the decrease of life in the case where the imposed strain amplitude is high. According to the analysis based on energy dissipation theory, this fatigue life decrease of the SMAT processed specimens could be due to the higher energy dissipation rate in the SMAT affected region

Etude de la déformation des microstructures génériques des alliages TiAl sous sollicitation cyclique à température ambiante et haute température : effet Bauschinger et viscosité

International audienceThe cyclic deformation of four TiAl common microstructures is studied experimentally at room and high temperature. Multilevel and multirate tests are performed to highlight the microstructure impact on the Bauschinger effect and the strain rate sensitivity. The mechanical behaviors are linked to their corresponding deformation mechanisms. Results can directly be used to develop microstructure-sensitive modeling of the mechanical behaviors of TiAl alloys