Simulation-aided Design of Thread Milling Cutter

AbstractThread milling has become quite popular in recent years as an alternative to tapping or other forms of threading because of diversity and complexity of parts and flexibility of the process in industries such as biomedical applications, aerospace and die-mold manufacturing. Today the design of the tooth profile is, however, predominantly feasible by the expertise and “trial and error” principle. Presented in this paper are a novel methodology to design the tooth profile of the thread mill by comparing the “to-be” thread profile and the “as-is” thread profile which is analyzed by means of NC cutting simulation. The simulation kernel enables to continually subtract the swept volume of thread milling cutter undergoing helical movement from the workpiece and to calculate the virtual workpiece (VWP). Combined with the standardized “to-be” thread profile, the tooth profile of to-be-designed thread mill is adaptively modified until the thread profile on VWP and the “to-be” thread profile become congruent with each other. The proposed methodology could be integrated into CAD/CAM systems

Phase-field modeling of crack propagation based on multi-crack order parameters considering mechanical jump conditions

The phase field method is commonly used for the crack propagation modeling in modern material science, as they allow for an implicit tracking of the crack surface. However, most of these crack propagation models are for homogeneous materials, and there exist only a few approaches for heterogeneous systems. Recently, Schöller et al. [1] presented a novel phase-field model for multiphase materials, e.g. composites, based on multi-crack crack order parameters. Despite the quantitative advantages of the model, it is based on a simple scheme for the underlying homogenization problem. In this work, a more advanced homogenization scheme based on mechanical jump condition is applied to the model. Consideration of these jump conditions yields phase-specific stresses and strains. Therefore, the mechanical driving force for crack propagation can be modeled as more independent of the elastic properties of other physical regions. Volume elements of a fiber reinforced polymer are used to demonstrate the limitations of the simple scheme, as well the improvement if considering mechanical jump conditions. Thereby, the contrast in the crack resistance of the two materials is varied. It is shown that the simple linear interpolation does not lead to reasonable crack paths for contrary contrasts of elastic modulus and crack resistance. Taking into account the mechanical jump conditions instead yields still reasonable results. For both the final crack paths and the stress-strain curves of the system, the novel model is less sensitive to a change in fiber crack resistance. While the result of the simple scheme depend on the selected fiber crack resistance, although failure of the matrix is expected

Phase-inherent linear visco-elasticity model for infinitesimal deformations in the multiphase-field context

A linear visco-elasticity ansatz for the multiphase-field method is introduced in the form of a Maxwell-Wiechert model. The implementation follows the idea of solving the mechanical jump conditions in the diffuse interface regions, hence the continuous traction condition and Hadamard’s compatibility condition, respectively. This makes strains and stresses available in their phase-inherent form (e.g. $\varepsilon ^{\alpha }_{ij}$, $\varepsilon ^{\beta }_{ij}$), which conveniently allows to model material behaviour for each phase separately on the basis of these quantities. In the case of the Maxwell-Wiechert model this means the introduction of phase-inherent viscous strains. After giving details about the implementation, the results of the model presented are compared to a conventional Voigt/Taylor approach for the linear visco-elasticity model and both are evaluated against analytical and sharp-interface solutions in different simulation setups

Phase-field investigation on the microstructural evolution of eutectic transformation and four-phase reaction in Mo-Si-Ti system

By using phase-field method, we investigate the morphological evolution of three-phase eutectic transition and four-phase reaction in Mo-Si-Ti system through 2-D and 3-D simulations. For the eutectic transition, we focus on the two-phase growth of lamellar pair from an isothermally undercooled melt: $L → Ti(Mo)_5Si_3 +(Mo,Si,Ti)$, and obtain a microstructure selection map for (m_) stable, (m$_{}$) unstable, and (m$_{}$) oscillatory growth (metastable mode), in terms of the Mo-composition and lamellar spacings. The underlying reason for these three different morphologies is clarified by analyzing the growth rate of the solidification front. In addition, we scrutinize the influence of interfacial energy on the solidification morphology and observe three different types of growth mode: (g_) curving, (g$_{}$) stable, and (g$_{}$) unstable growth. For the four-phase reaction, $L + Mo(Ti)_3Si → Ti(Mo)_5Si_3 + (Mo,Si,Ti)$, we observe the remelting of $Mo(Ti)_3Si$ phase and the formation of a lamellar pair consisting of $Ti(Mo)_5Si_3 and (Mo,Si,Ti)$ on the surface of the $Mo(Ti)_3Si$ phase after an interface of the lamellae pair phases is formed. A certain orientation angle with respect to the solidification direction is obtained for the lamellar pair growth during the four-phase reaction. In both eutectic phase transformation and four phase reaction, a comparison between the 2D and 3D simulations reveals the influence of the third dimension on the development of the lamellar pair

Wicking in Porous Polymeric Membranes: Determination of an Effective Capillary Radius to Predict the Flow Behavior in Lateral Flow Assays

The working principle of lateral flow assays, such as the widely used COVID-19 rapid tests, is based on the capillary-driven liquid transport of a sample fluid to a test line using porous polymeric membranes as the conductive medium. In order to predict this wicking process by simplified analytical models, it is essential to determine an effective capillary radius for the highly porous and open-pored membranes. In this work, a parametric study is performed with selected simplified structures, representing the complex microstructure of the membrane. For this, a phase-field approach with a special wetting boundary condition to describe the meniscus formation and the corresponding mean surface curvature for each structure setup is used. As a main result, an analytical correlation between geometric structure parameters and an effective capillary radius, based on a correction factor, are obtained. The resulting correlation is verified by applying image analysis methods on reconstructed computer tomography scans of two different porous polymeric membranes and thus determining the geometric structure parameters. Subsequently, a macroscale flow model that includes the correlated effective pore size and geometrical capillary radius is applied, and the results are compared with wicking experiments. Based on the derived correction function, it is shown that the analytical prediction of the wicking process in highly porous polymeric membranes is possible without the fitting of experimental wicking data. Furthermore, it can be seen that the estimated effective pore radius of the two membranes is 8 to 10 times higher than their geometric mean pore radii