Advances in Industrial and Manufacturing Engineering最新文献

Grinding is a finishing process typically done in most metallic manufacturing centers, primarily to achieve precision and surface improvement. Currently, the grinding process of titanium alloys generally requires flood coolant application. Electron Beam Powder Bed Fusion (EB-PBF) is an additive manufacturing process that uses an electron beam as the heat source to melt and fuse powder particles to build layer by layer to build a three-dimensional component. Grinding is a major secondary process applied to additively manufactured metals, but with the current methodologies, grinding may impart tensile residual stress on the surface, and thus the performance of the material under fatigue conditions is reduced. In this paper, a targeted cutting fluid application approach for grinding an additively manufactured titanium alloy is used to possibly impart a compressive residual stress upon the subsurface while also providing an improved surface roughness. This study uses samples ground with a traditional flood coolant and samples with targeted cutting fluid applications developed by the researchers. Metrics such as surface residual stress, surface roughness, microstructure, and microhardness were used to determine imparted qualities using the various grinding cooling methodologies. The results show that the subsurface maximum principal residual stresses decreased by 108%, the average surface roughness decreased by 33%, and the microhardness at 5 μm increased by 1% using targeted air as the cutting fluid compared to flood cooling while grinding additively manufactured Ti6Al4V. Overall, the targeted grinding cooling fluid application induced compressive subsurface residual stresses and reduced the average surface roughness.

The performance of formed components is significantly influenced by the initiation of ductile damage. Preceding forming operations, for instance, affect the service life determined in fatigue tests. In the current investigation, the effect of ductile damage in forming is isolated by changing the shoulder opening angle in forward rod extrusion. Forming-induced ductile damage is then related to measurements of void area fraction, density and Young’s modulus. Subsequent fatigue tests in the low cycle range indicate that the service life of the extruded components can be improved through a reduction of the forming-induced damage. A novel constitutive model considering forming-induced damage and fatigue damage is proposed to account for the observed behavior in axial fatigue tests of extruded components. The non-local ductile damage formulation is formulated in the framework of Generalized Standard Materials. Kinematic and isotropic hardening are considered. Based on earlier work of Lemaitre and Desmorat, the fatigue damage initiation criterion is extended to take the observed mechanical behavior in low cycle axial fatigue tests of formed components into account. The extended model is able to capture the effect of forming-induced damage on the service life.

In the paper new biaxial specimen geometries for thin ductile sheet metals are proposed. The design focuses on the stress-dependent damage and failure behavior. A plastic anisotropic material model based on Hill’s yield criterion and corresponding associated flow rule is presented and the related material parameters are given. Accompanying numerical simulations reveal the stress state and relate the damage mechanisms to the loading condition. The different proposed specimen geometries indicate various effects on the localization of inelastic strains, the material orientation as well as on the damage and fracture processes. During the biaxial tests strain fields in regions of interest are monitored by digital image correlation and after the experiments pictures of the fracture surfaces are taken by scanning electron microscopy and related to the stress dependent damage and failure precesses. The experimental and numerical results demonstrate the high potential of the newly developed biaxially loaded specimens.

This work establishes a computational framework for the quantification of the effect of uncertainty of material model parameters on extremal stress triaxiality and Lode angle values in plastically deformed devices, whereby stress triaxiality and Lode angle are accepted as key indicators for damage initiation in metal forming processes. Attention is paid to components, the material response of which can be represented as elasto-plastic with proportional hardening as a prototype model, whereby the finite element method is used as a simulation approach generally suitable for complex geometries and loading conditions. Uncertainty about material parameters is characterized resorting to probability theory. The effects of material parameter uncertainty on stress triaxiality and Lode angle are quantified by means of a variance-based global sensitivity analysis. Such sensitivity analysis is most useful for apportioning the variance of the stress triaxiality and Lode angle to the uncertainty on material properties. The practical implementation of this sensitivity analysis is carried out resorting to a Gaussian process regression, Bayesian probabilistic integration and active learning in order to decrease the associated numerical costs. An example illustrates the proposed framework, revealing that parameters governing plasticity affect stress triaxiality and Lode angle the most.

This paper gives insight into the development and utilization of a computer software that uses raw experimental data from the load cells and DIC systems to obtain the instant of time at fracture $t_f$, the loading paths in principal strain space ${\epsilon }_1=f\left({\epsilon }_2\right)$, and their conversion into the space of effective strain vs. stress triaxiality $\bar{\epsilon }=f\left(\eta \right)$. Special emphasis is given to the different assumptions and stress triaxiality measures that can be used to convert the loading paths from principal strain space into the space of effective strain vs. stress triaxiality. Results for double-action radial extrusion show the differences of treating the loading paths as linear or non-linear from beginning until the onset of failure by fracture. Results also allow concluding on the importance of accounting for the stress triaxiality derived from individual experimental measurements in an average sense over the entire loading paths, to avoid overestimation and mislocation of the fracture forming limits. The applicability of the software for education and training of students in formability is also discussed.

This paper investigates the possibility of using empirical tool life models to predict tool life in a side milling application in a medium carbon steel, C 45E. To do this, an extensive dataset containing 46 data points with different machining parameters are produced. Four different empirical models: Taylor’s equation, Colding’s equation and Extended Taylor both using depth of cut and feed as well as an Extended Taylor using equivalent chip thickness has been considered. It is found that Colding’s equation is best suited to predict the tool life for this application. Furthermore, this paper suggests a novel method to fit the experimental data to the empirical models. Based on the results from previously published papers it is shown that the proposed method performs equally or better to determine the model constants.

Elastomers play a significant role across different fields including healthcare. They have similar mechanical properties to some of the soft tissues of the human body, which makes them useful in applications such as implants and prosthetics. However, forming elastomers for tailored-fit medical devices using 3D printing is still not yet widely utilized because of the current problems seen as innate to the elastomer properties, and the principles of 3D printing techniques. With a focus on silicone and polyurethane, this review details the state-of-the-art 3D printing techniques that are being modified over the years to allow its printability for medical applications. The paper also discusses the manufacturing challenges faced by the researchers in printing elastomers, and how these challenges are currently being addressed. This review paper shows further research direction and hopes to initiate further development of these solutions. This will allow the 3D printing of elastomers to gain widespread use in patient-specific medical devices and components with optimized functionality in the near future.

Forward rod extrusion experiments with high extrusions strains show a decrease of void area during forming. Most of the established damage modelling approaches have been developed without that knowledge and do not adequately cover the effect of void closure. Furthermore, many so called coupled models focus on the effect of ductile damage on the plastic flow of the material which results in more complex and numerically expensive models. But the effect of voids on plastic flow is insignificant for many cold forging applications, as shown in recent experiments. Thus, an uncoupled model is proposed that covers the effects of void nucleation, growth and closure. The proposed model is calibrated using void area fractions measured in forward rod extrusion experiments. A validation for various load paths shows good accordance with experimental data for void closure conditions under low triaxiality as well as for void evolution under higher triaxialities.

Manganese sulphide inclusions are commonly found in steels and known to facilitate the formation of deformation-induced damage sites in the form of voids during cold forming. These damage sites either exist as cracks, splitting the inclusion in two parts, or as delamination, separating the inclusion from the surrounding steel matrix. Both negatively influence the longevity of components, especially under cyclic loading. The analysis of damage is inherently scale-bridging, ranging from deteriorated global mechanical properties of the finished part, over the damage behaviour of individual inclusions, to the local description of individual voids. In this work, we set out to devise an analysis approach gathering information on all these scales. To this end, we conducted in-situ tensile tests while acquiring high resolution SEM panoramic images and analysed them with two neural networks, trained for this work, to detect damage sites with respect to the inclusions at which they nucleated. We find that the main damage mechanism during tensile deformation parallel to the length of inclusions is cracking and that damage evolution is equally influenced by void nucleation and void growth in the observed range of deformation. By focussing on the damaging behaviour of different inclusions, we show that the position of inclusions in the microstructure influences the resulting damage evolution and that the vicinity of pearlite bands leads to decreased damage formation.

Steels with high carbon content can hardly or not at all be welded, but are of great interest for cladding applications due to their high hardness. In this study, the influence of process parameters on weld seam geometry and process stability is investigated when welding AISI 52100 bearing steel using the laser hot-wire cladding process. Process stability is evaluated using actual and set values for the wire feed rate and current parameters to determine a process window for a stable welding process. Weld seams are measured and analyzed in terms of width, height, contact angle, and shape. The effect of the process parameters on the weld seam geometry is investigated and appropriate mathematical functions to describe the geometry are determined. Process parameter sets in the range of 1-2 m/min wire feed rate and 45-75 A hot wire current were investigated. Unstable parameter sets occur clustered at high wire feed rate of 2 m/min for all hot wire currents. In addition, the process is unstable at high hot wire current of 75 A and low wire feed speed of 1 m/min. The remaining parameter sets resulted in a stable process. The investigated functions parabolic, cosinusoidal and circular arc for the mathematical description of the weld seam geometry, no clearly significant result could be determined. Only a trend towards the circular arc function and the parabolic function is apparent.