A finite element (FE) simulation model is presented in order to serve as a fast prediction tool for the surface layer characteristics after shot peening. This includes a FE-geometry model and an ...elasto-viscoplastic combined isotropic kinematic material. For the detailed validation of its applicability simulated and experimentally measured topographies and residual stresses on plates of AISI 4140 in a quenched and tempered state after single and double impacts of large hardened steel balls will be compared. These large shot experiments allow a high resolution of the residual stress state of single dimples by X-ray measurements and eliminate the statistical influence of multiple impacts. Finally the residual stress profiles of differently shot peened samples of the same material will be compared with accordingly simulated results.
Modelling of laser surface hardening of AISI 4140 steel including the effect of inhomogeneous austenite formation due to locally different austenizing and quenching conditions is carried out to gain ...a better understanding of the material reaction during short-time hardening processes. Dilatometric studies at high heating and cooling rates lead to base informations for material laws reflecting the influence of the inhomogeneity of austenite on the quenching process. They were implemented in the finite-element-program ABAQUS as user defined material laws and allow a coupled calculation of temperature and phase development during heating and cooling. The influence of heating rate and cooling rate on the time-dependent temperature fields and phase transformations within the affected zone was investigated. A good correspondence between the results of simulation and experimental data was obtained in respect of the resulting hardness profiles and the degree of homogeneity of the hardened structure.
The statistics of Young’s modulus of microspecimens subjected to a tensile load is examined experimentally, numerically and analytically. The material considered is Stabilor
®G, a dental alloy, ...mainly consisting of gold. Tensile tests with microspecimens produced by vacuum pressure casting have been performed using a self-designed universal micro-testing machine. The numerical approach is based on the finite element method with the microstructure being described by a periodic Voronoi tessellation with randomly oriented grains. The analytical approach uses an explicit formulation of the singular approximation in terms of texture coefficients and is valid for arbitrary sample symmetries. It is found that the finite element approach and the analytical approach reproduce the experimental findings. Furthermore, it is shown that the mean value and the standard deviation of Young’s modulus of microspecimens made of cubic crystals subjected to tensile loads can be described by a unified scaling law. The results imply that the statistics of apparent properties of cubic crystal aggregates can be determined using anisotropic effective medium approximations.
The use of aluminium in lightweight profiles for vehicle spaceframes is state of the art due to the material's low density combined with good specific mechanical properties. Nevertheless, the ...absolute stiffness and strength of aluminium is rather low in comparison to steels. A possibility to increase both stiffness and strength of aluminium-based structures is the use of compound-extruded profiles in which high-strength metallic reinforcements are incorporated. Within the scope of the present investigations, compound-extruded profiles with wire-reinforcements made of stainless spring steel 1.4310 (X10CrNi18-8), nickel-base superalloy Inconel 718 or cobalt-base alloy Haynes 25 in an AA6060 aluminium matrix were characterized in terms of the debonding shear strength using the push-out-technique. In addition to varying the reinforcement materials, the investigations focussed on the influence of different chemical and mechanical pre-treatments.
For the production of small quantities of micro devices, machining is a low cost alternative to lithographic processing techniques. However, machining shows process specific size-effects upon ...miniaturization to the micrometer regime. Hence, the orthogonal turning process is chosen to study the influence of process parameters like uncut chip thickness h, cutting velocity v
c
and cutting edge radius r
β
on the cutting force and the surface plastification by two-dimensional, thermo-mechanically coupled finite element simulations. A rate-dependent plasticity law is used for investigation of a normalized medium carbon steel (AISI 1045). Furthermore, the characteristics of the influences of the different parameters are analyzed mathematically by similarity mechanics. In particular, the frictional effects on the cutting process are studied in detail using a friction coefficient μ based on experimental results, and the influences of the process parameters on the cutting force and the plastic deformation of the surface layer are determined numerically. These results are compared with experimental measurements. The specific cutting forces are analyzed and discussed in detail. Size-effects observed experimentally are also found by numerical simulations.
The lifetime of ceramic thermal barrier coatings (TBCs) is significantly affected by the growth of a dense alumina scale at the interface between TBC and the bond coat (BC), the so-called thermally ...grown oxide (TGO). Occurring growth stresses and thermal expansion mismatch can lead to system failure by spalling and delamination. The evolving stress state depends crucially on BC oxidation kinetics, TGO creep behavior and thermal–mechanical properties of the coating materials. Using a finite element model of a TBC system, the influence of TGO creep on the stress development was studied. The performed calculations consider the effect of TGO grain size, the roughness of the TBC/bond coat interface as well as time and temperature-dependent oxide growth. A high temperature induced sintering of the TBC is also taken into account. The obtained results show an oxidation induced development of compressive stresses above the peaks and of tensile stresses in the valleys of the rough TBC/BC interface. The results indicate that TGO creep can cause a significant stress relaxation above 1050
°C for grain sizes of 0.1
μm. At 1100
°C creep stress relaxation can already be expected for a grain size of 0.3
μm.
The miniaturization of cutting processes shows process specific size-effects like the exponential increase of the specific cutting force k
c
with decreasing depth of cut h. Experiments were carried ...out in an orthogonal turning process. The influence of different process parameters on the results was investigated separately to identify process specific size-effects. Two materials were studied: a normalized steel AISI 1045 and an annealed AISI O2. To complement the experiments, parameter variations were performed in two-dimensional, thermo-mechanically coupled finite element simulations using a rate-dependent material model and analyzed by similarity mechanics. The influence of rounded cutting-edges on the chip formation process and the plastic deformation of the generated surface were determined numerically. The complex physical effects in micro-cutting were analyzed successfully by finite element simulations and compared to experiments.
In recent years laser surface hardening using pulsed laser sources has become an increasingly established technology in engineering industry and has opened up wider possibilities for the application ...of selective surface hardening. However, the choice of the process parameters is generally based on experience rather than on their empirical influence on the resulting microstructure, and for hardening processes with cyclic temperature changes, almost no correlations between process parameters and hardening results are known. Therefore, some problems regarding the choice of the process parameters and their influence on the resulting microstructure still remain. In particular, there is a lack of data concerning the effect of cyclic temperature changes on hardening. To facilitate process optimization, this paper deals with a detailed characterization of the microstructures created in quenched and tempered AISI 4140 (German grade 42CrMo4) steel following a temperature-dependent laser surface hardening treatment. The structure properties were obtained from microhardness measurements, scanning electron microscopy investigations and X-ray diffraction analysis of retained austenite.
Manufacturing of ceramic and metallic micro components in micro powder injection moulding (μPIM) requires mould inserts offering high wear resistance and a sufficient demoulding behaviour. Within the ...frame of this research μPIM mould inserts made from low and high alloyed tool steel were structured by micro milling and finished by micro peening and ultrasonic wet peening. Influence of surface condition on wear and demoulding behaviour of the steels in μPIM with ceramic feedstock was characterized using a laboratory tribotester simulating powder injection moulding and a specially adapted static friction tester. Results indicate that performance of mould inserts in micro powder injection moulding depends not only on hardness, surface condition and homogeneity of the mould insert materials but also is strongly influenced by the characteristics of the feedstock, like composition of the binder or amount and hardness of the ceramic particles.
