Experimental investigation and 3D finite element simulation of the turning process for AISI304 stainless steel

In this study, experimental investigations and simulations were conducted to examine the influence of machining parameters during the turning process of C45 medium carbon steel, with the simultaneous application of the Johnson-Cook plasticity model and Johnson-Cook damage model. The validity of the computational results was confirmed by comparing them with experimental findings on chip morphology and temperature rise during cutting. The obtained results indicate that cutting depth significantly affects chip morphology during the turning process, while cutting speed has a minimal impact on the chip length at a cutting depth of 1 mm. Additionally, the temperature rise during cutting is primarily concentrated around the cutting tool nose, rather than near the chip or machined surface. Among the investigated cutting speeds, 0.46 m/s is identified as the most suitable for turning C45 steel at a cutting depth of 1 mm. Finally, for practical purposes, an artificial neural network model based on machine learning is developed to predict the average temperature near the turning insert nose.

The paper presents results of the experimental investigation of deformation behavior and damage accumulation kinetics in a heat-resistant reactor pressure vessel steel at high stress levels under stress-controlled (pulsating), low-cycle loading up to 104 cycles. Hardness measurements have been performed upon various operating time periods under elastoplastic deformation. It has been found that hardness and strength of the steel exhibit qualitatively different behaviors throughout the lifetime. The damage accumulation process in steels under static and cyclic loadings has been studied by means of the LM-hardness method. The curves of Weibull homogeneity coefficient vs. cycling stress and accumulated strains are obtained.

Experimental investigation and statistical optimisation of the selective laser melting process of a maraging steel

Ultra-high-strength quenching and partitioning (Q&P) steels have achieved remarkable lightweight effect in automotive manufacture due to the excellent mechanical performances. However, the problem of sheared-edge cracking greatly limits their application. In this work, the damage generated in the shearing process of QP980 steel is experimentally investigated via microstructure characterization and micro-/macromechanical property evaluation. Moreover, the shearing deformation is simulated with six widely used damage models. The experimental results reveal that microvoids, microcracks, and work-hardening behavior are the main damage factors affecting the formability of sheared edges. Microvoids mainly formed at phase interfaces have a small size (≤5 μm), while microvoids generated from inclusions with a small number have a large size (>5 μm). As deformation continuously grows, microvoids distributed around the sheared surface are split into microcracks, which act as crack initiators in the subsequent forming step. Additionally, the highest microhardness in the fracture zone further enhances the susceptibility of edge cracking. Furthermore, the optimum damage model for QP980 steel was determined by developing user-defined subroutine VUSDFLD in Abaqus, which can be used in the prediction of fracture behavior of QP980 steel to reduce the risk of edge cracking.

Experimental Investigation and FE Simulation of Heat Affected Zone in Water-Jet Assisted Underwater Laser Cutting Process of Mild Steel and Titanium

Recent work on analogue CO2 storage sites has shown that the single most defining natural factor as to whether the store can be successfully utilised to retain 99% of the injected CO2 for 1000 years is the behaviour of fractures within the low permeability strata acting as caprock. Here we present experimental and numerical investigation of the hydro-mechanical behaviour of a natural fracture in a caprock during the flow of supercritical CO2 through it. The caprock is a naturally fractured dolomitic limestone sample recovered from a depth of ∼1500m, and is the primary seal to the natural CO2 storage analogue, the Fizzy field, in the Southern North Sea. For the first time the hydro mechanical behaviour of the fracture is examined using unique experimental equipment applying multiple high pressure single phase supercritical CO2 fluid flow experiments at representative in situ reservoir pressures (10–30MPa, with confining pressures from 35MPa to 55MPa) and a temperature of 40°C. The fracture surfaces are scanned to provide high resolution images both prior to and after the experimental investigation. The results are modelled through the further development of a hybrid numerical analytical approach to fluid flow through a discrete fracture, implemented in the open source code OpenGeoSys. The work indicates that through the statistical approximation of the fracture surface and combination of the application of standard nonlinear flow models and analytical mechanical solutions, the key features of the hydro-mechanical behaviour of the supercritical fluid flow through the sample can be replicated. The results provide insight into erroneous effective stress assumptions at higher fluid pressures and the importance of understanding the coupled process multi-physics behaviour of fractures in a CO2 storage setting. Over-simplistic approximations using the effective stress law lead to a Biot's coefficient greater than 1 being predicted under varying fluid and confining pressures.

Influence of geometrical parameters on the flow characteristics of multi-pipe earth-to-air heat exchangers – experimental and CFD investigations

Nanoscratch testing is a highly reliable method used to extract a variety of film properties. It is proven that many of the experimental factors can influence the obtained results, such as the probe tilt, the scratch depth, etc. On the other hand, the surface roughness of the samples is an important parameter in nanoscratch and other similar tests, including the nanoindentation test. Thus, the effect of surface roughness on both the nanoscratch experiments and finite element simulations has been investigated. By performing scratch tests on gold and copper films and carrying out the finite element (FE) simulations on the rough and smooth surfaces, the importance of surface morphology was studied. The results indicate that the FE models consisting of the films with rough surfaces can lead to more accurate results, compatible with the experimental data. It was also revealed that the impact of surface morphology on the extracted friction coefficient tends to lose its significance in higher scratch depths. However, comparing the experimental results and simulation data, at lower scratch depths due to the presence of van der Waals forces the FE simulations will not lead to precise results.

The seismic performance of structures could be enhanced by the inclusion of supplemental components that dissipate the earthquake-induced energy. This is especially crucial for rocking structures that possess low energy dissipation properties due to their damage avoidance mechanism. Amongst variously developed yielding-type energy dissipaters (EDs), buckling-restrained energy dissipating carbon steel bars have received considerable attention as they make the most use of the inherent energy dissipation of steel and are easy to fabricate. However, maintenance, repair costs, and performance disruptions owing to corrosive environments have been mostly disregarded in past investigations. Employing stainless steel can be a viable solution to overcome such issues. The work described in this two-part study sheds light on various aspects of the buckling-restrained stainless steel EDs through experimental and finite element (FE) investigations. The mechanical properties of type 304L stainless steel including uniaxial monotonic response, strain sensitivity, and cyclic hardening are characterized. It is shown that the material possesses high ductility along with substantial hardening characteristics. In the first phase of testing, energy dissipating bars with different fuse diameters and lengths are designed. Load and strain capacities and bar-tube interactions of the buckling-restrained energy dissipation device are studied through quasi-static tests. In the second phase of testing, various EDs are designed, fabricated with stainless and mild steel, and tested under quasi-static loading to validate the findings of the FE investigations. The test results demonstrate a stable hysteresis response of the buckling-restrained stainless steel EDs with a cyclic average strain capacity of 10%. The FE modelling procedure, calibration, and parametric studies are presented in the companion paper as Part II.

Experimental and numerical investigations on the performance evaluation of shear deficient and GFRP strengthened reinforced concrete beams

Preclinical wear evaluation is extremely important in hip replacements, wear being one of the main causes of failure. Experimental tests are attractive but highly cost demanding; thus predictive models have been proposed in the literature, mainly based on finite element simulations. In such simulations, the effect of friction is usually disregarded, as it is considered not to affect the contact pressure distribution. However, a frictional contact could also result in a shift of the location of the nominal contact area, which can thus modify the wear maps. The aim of this study is to investigate this effect in wear prediction for metal-on-metal implants. Wear assessment was based on a purpose-developed mathematical model, extension of a previous one proposed by the same authors for metal-on-plastic implants. The innovative aspect of the present study consists in the implementation of a modified location of the nominal contact point due to friction, which takes advantage of the analytical formulation of the wear model. Simulations were carried out aimed at comparing total and resurfacing hip replacements under several gait conditions. The results highlighted that the adoption of a frictional contact yields lower linear wear rates and wider worn areas, while for the adopted friction coefficient (f=0.2), the total wear volume remains almost unchanged. The comparison between total and resurfacing replacements showed higher scaled wear volumes (wear volume divided by wear factor) for the latter, in agreement with the literature. The effect of the boundary conditions (in vivo versus in vitro) was also investigated remarking their influence on implant wear and the need to apply more physiological-like conditions in hip simulators. In conclusion although friction is usually neglected in numerical wear predictions, as it does not affect markedly the contact pressure distribution, its effect in the location of the theoretical contact point was observed to influence wear maps. This achievement could be useful for increasing the correlation between numerical and experimental simulations, usually based on the total wear volume. In order to improve the model reliability, future studies will be devoted to implement the geometry update by combining the present model to finite element analyses. On the other hand, further experimental investigations are required to get out from the wide dispersion of wear factors reported in the literature.

The paper presents results of FEM modelling as well as properties and microstructure of the ultralow-carbon ferritic steel after the unconventional SPD process—DRECE (dual rolls equal channel extrusion). Based on the conducted numerical simulation information about the deformation behaviour of a steel strip during the DRECE process was obtained. The simulation results were experimentally verified. The influence of DRECE process on hardness distribution, fracture behaviour and microstructure evolution of the investigated steel was analysed. The increase of steel strength properties after subsequent deformation passes was confirmed. The microstructural investigations revealed that the processed strips exhibit the dislocation cell microstructure and subgrains with mostly low-angle grain boundaries. The grains after processing had relatively high dislocation density and intense microband formation was observed. It was also proved that this unconventional SPD method fosters high grain refinement.

Residual stresses in components are a central issue in almost every manufacturing process, as they influence the performance of the final part. Regarding hot forming processes, there is a great potential for defining a targeted residual stress state, as many adjustment parameters, such as deformation state or temperature profile, are available that influence residual stresses. To ensure appropriate numerical modeling of residual stresses in hot forming processes, comprehensive material characterization and suitable multiscale Finite Element (FE) simulations are required. In this paper, experimental and numerical investigations of thermo-mechanically processed steel alloy 1.3505 (DIN 100Cr6) are presented that serve as a basis for further optimization of numerically modeled residual stresses. For this purpose, cylindrical upsetting tests at high temperature with subsequently cooling of the parts in the media air or water are carried out. Additionally, the process is simulated on the macroscale and compared to the results based on the experimental investigations. Therefore, the experimentally processed specimens are examined regarding the resulting microstructure, distortions, and residual stresses. For the investigation on a smaller scale, a numerical model is set up based on the state-data of the macroscopic simulation and experiments, simulating the transformation of the microstructure using phase-field theory and FE analysis on micro- and meso-scopic level.

Investigation of Machinability Responses During Magnetic Field Assisted Turning Process of Preheated Mild Steel

Experimental investigation and optimization of turning process of EN8 steel using Taguchi L9 orthogonal array