In bonding processes, the final distribution of the adhesive in the gap depends on the compressing normal load, velocity and kinematics, the adhesive properties, but above all on the initial adhesive distribution. The latter is also largely responsible for trapped air and the adhesive squeezes out at the edges. A model has recently been developed for the simulation of the flows during compression processes in adhesively bonded joints. This paper extends the aforementioned model towards shear rate-dependent viscosity, a phenomenon crucial for most industrial adhesives. Besides the assumption of a Newtonian fluid, approximations of a power-law and a Yasuda law are used. For this purpose, a further subordinate Newton method for determining the flow profiles is added to the existing model. Rheological measurements over a wide range of shear rates serve as a reference. For the verification, studies are performed on two academic examples: a rectangular, and a circular propagation. The results are compared with analytical solutions and CFD simulations. A very good agreement of pressure (deviations below 1.5%), and velocity profiles (deviations below 5%), for all scenarios and flow laws, was found. The long-term goal of this model development is the prediction of adhesive compression flows for complex application patterns.

Starved lubrication is an important strategy for minimizing the amount of lubricant needed, and also inevitably occurs during idling and fail-safe lubrication. In this regime, however, the flow of the lubricant and the related friction coefficients are yet to be fully understood. This research aims to make fundamental contributions to the understanding of contact mechanics of partially lubricated contacts. Recent experiments with a pin-on-disk tribometer examined the microscopic behavior of partially filled gaps. Using a new experimental setup on a macroscale, new insights into partially filled gaps with rough surfaces were gained. This work presents the systematic analyses of the lubricant flow, friction coefficients, and other variables over a wide range of friction parameters. Distinct friction behaviors were observed, and similar effects occur on both the micro and macroscale. The experimental results show that a typical Stribeck characteristic is visible regarding not only the relative velocity, but also regarding the lubricant filling level in the gap. The fluid exhibits a variety of flow patterns for various velocities and viscosities. The patterns relate to different friction regimes, such as dry friction and mixed lubrication. It is concluded that the filling level is a valid parameter for regulating the transition from dry friction to hydrodynamic lubrication. These findings are quantified regarding the filling level and it is shown that for the identification of the friction regimes the filling level is an independent parameter in addition to the established parameters like speed, viscosity and pressure.

In most bonding processes, an adhesive is applied to a substrate in a specific pattern before the second substrate is subsequently pressed against it. During this, the adhesive flows in such a way that, ideally, it completely fills the joint. In practice, however, areas with entrapped air frequently remain in the bonded adhesive layer. Within the scope of a research project, these flows are systematically analyzed in order to identify optimal initial application patterns for the adhesive and substrate geometry to minimise such risks. For this purpose, the authors use an efficient flow model, the partially filled gaps model (PFGM), extended in this study to include the functionality of trapped air pockets. Depending on the volume fractions of air and adhesive, the flow of both phases is computed. Therefore, the model is introduced and fully described, benchmarked with respect to its plausibility and functionality, and results obtained are compared with a CFD calculation. Thereafter, the functionality of openings and closings of the pockets are analyzed. Lastly, the model is then applied to a real scenario created with a Hele–Shaw cell measurement. The benchmark as well as the comparison with the measurement results show the high potential of this technique.

Currently, adhesive bonding processes are developed and optimised in a time-consuming trial and error procedure, which rarely leads to an optimal solution due to the high complexity of the adhesive flow behaviour during application. The ideal adhesive layer has precise geometric specifications; entrapped air bubbles or overfilling of the bond should be avoided. Numerical methods, such as Computational Fluid Dynamics (CFD), are only capable of calculating squeeze-flow processes to a limited extent. Apart from high computing times, mesh and convergence problems often occur due to the small ratio of adhesive layer thickness to adhesive layer length and width. The Generalised Partially Filled Gap (GPFG) model, published in a companion paper uses fundamental characteristics of every bonding process to derive clever assumptions, and thus provide an efficient simulation tool for adhesive squeeze-flow. The GPFG model simplifies the squeeze-flow to a two-dimensional problem, as the flow in thickness direction can be neglected for most bonding processes – without significant loss of accuracy compared to analytical or CFD solutions. The experimental validation of the model is presented in this study. Both stresses and flow geometry were evaluated, and a very good agreement between experiments and model was proven.

Binder jetting holds great potential for revolutionizing conventional production processes for high-performance components. However, current applications face significant challenges regarding the depowdering and cleaning of complex internal geometries. A novel approach to these challenges is splitting the desired component into smaller, easy-to-clean parts and using sinter bonding to achieve the desired shape. This greatly reduces manual cleaning and preparation time during the production since sintering is required in any case. The sinter joint is currently significantly weaker than the rest of the part and may pose a risk of failure. This study focuses on the effects of different parameters that influence the joint strength and the contact surface between two parts. With different experimental setups, a variety of influences is identified and quantified: depowdering air pressure, component orientation in the build box, initial contact pressure between the green parts, and macroscopic component deformation. The experimental results are supported by a modified Boussinesq contact model. Combining experiments and simulations, it was found that the relative contact between two green parts varies between 5 and 26%, depending on the parameter set used. In this study, the authors introduce the idea of two-part manufacturing in metal binder jetting and subsequent joining of the components in the sintering process.

Modeling tribological contacts is commonly based on the Reynolds equation. This study discusses the validity of conventional, averaged Reynolds simulations for systems including starvation regimes. Two fundamental assumptions that are used as common practice in many elasto-hydrodynamic (EHD) calculations, are debated. First, the use of a cavitation pressure (in most cases assumed to be zero) independent of the microscopic roughness. Second, the application of a shear flow factor, which is determined on a microscopic scale with a fully filled gap. The validity of these two assumptions is analyzed with simulations on the microscopic scale. For this purpose, simulations of partially filled contacts are carried out using the partially filled gaps model developed by the authors. The topographies, the filling level and the fluid distribution were varied. The simulations comply with established models for the fully filled state and show a distinct behavior for partial filling and different fluid distributions. Neglecting the contribution to pressure buildup and shear flow of partially filled domains is a valid method in most cases. However, as this study shows, near the fully filled regime, the domains should be handled with care.